[R] Help needed with aggregate or other solution

Jeff Newmiller jdnewmil at dcn.davis.ca.us
Thu Oct 26 17:07:40 CEST 2017


On Thu, 26 Oct 2017, Thomas Adams wrote:

> Hi Jeff,
> 
> Thank you for the suggestions -- I appreciate your help. Unfortunately, the
> result2 has two problems...
> 
> (1) there are now 3 date columns (it looks like 2 cols are merged into 1
> col)

No, there are two date columns. Result2 includes the grouping value as a 
row name (pulled from the names of the dta2list items by rbind).

> (2) the output rows should not have any of the basistime dates repeated
> (maybe I misstated the problem); I need the max fcst value by basistime, but
> also list the date value for that row; for example:

Then try out my code replacing

dta2list <- split( dta2, dta2$date )

with

dta2list <- split( dta2, dta2$basistime )

and

%>% group_by( date )

with

%>% group_by( basistime )

Please study how the code works and ask questions based on gaps in that 
knowledge rather than how the results are not what you expected. This 
mailing list is not a do-your-work-for-you coding service. Some help pages 
you should look at include:

?rownames
?split
?lapply
?do.call
?rbind
?group_by
?do

You might also find [1] helpful in general, and [2] helpful for 
understanding dplyr.

[1] H. Wickham, The Split-Apply-Combine Strategy for Data Analysis, 
Journal of Statistical Software, vol. 40, no. 1, Apr. 2011.

[2] H. Wickham and G. Grolemund, R for Data Science. OReilly UK Ltd, 2017. 
URL: https://r4ds.had.co.nz.

> 
>              basistime fcst
> 1   2012-01-25 15:02:00 47.9
> 2   2012-01-26 15:11:00 50.4
> 3   2012-01-27 01:41:00 46.0
> 4   2012-01-27 10:15:00 47.3
> 5   2012-01-27 15:15:00 47.3
> 6   2012-01-28 14:22:00 46.2
> 7   2012-01-29 13:33:00 45.8
> 8   2012-01-30 14:11:00 44.8
> 9   2012-01-31 14:24:00 43.9
> 10  2012-02-01 14:55:00 41.1
> 11  2012-02-02 14:56:00 38.1
> 12  2012-02-03 14:40:00 36.2
> 13  2012-02-04 15:01:00 34.7
> 14  2012-02-05 15:04:00 33.1
> 15  2012-02-06 14:37:00 32.2
> 
> This is very close to what I need. The basistime dates are all unique, with
> the max fcst value for the available basistime dates; but I additionally
> need the corresponding 'date' value.
> 
> Best,
> Tom
> 
> 
> 
> On Thu, Oct 26, 2017 at 1:28 AM, Jeff Newmiller <jdnewmil at dcn.davis.ca.us>
> wrote:
>       Thanks for the dput...
>
>       #### reproducible example of split-apply-combine ###
>
>       dta <- structure(list(date = structure(c(1L, 2L, 3L, 4L, 5L, 6L,
>       7L,
>       8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L, 19L, 20L,
>       5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L,
>       19L, 20L, 21L, 22L, 23L, 24L, 7L, 8L, 9L, 10L, 11L, 12L, 13L,
>       14L, 15L, 16L), .Label = c("2012-01-25 18:00:00", "2012-01-26
>       00:00:00",
>       "2012-01-26 06:00:00", "2012-01-26 12:00:00", "2012-01-26
>       18:00:00",
>       "2012-01-27 00:00:00", "2012-01-27 06:00:00", "2012-01-27
>       12:00:00",
>       "2012-01-27 18:00:00", "2012-01-28 00:00:00", "2012-01-28
>       06:00:00",
>       "2012-01-28 12:00:00", "2012-01-28 18:00:00", "2012-01-29
>       00:00:00",
>       "2012-01-29 06:00:00", "2012-01-29 12:00:00", "2012-01-29
>       18:00:00",
>       "2012-01-30 00:00:00", "2012-01-30 06:00:00", "2012-01-30
>       12:00:00",
>       "2012-01-30 18:00:00", "2012-01-31 00:00:00", "2012-01-31
>       06:00:00",
>       "2012-01-31 12:00:00", "2012-01-31 13:00:00", "2012-01-31
>       18:00:00",
>       "2012-02-01 00:00:00", "2012-02-01 06:00:00", "2012-02-01
>       12:00:00",
>       "2012-02-01 18:00:00", "2012-02-02 00:00:00", "2012-02-02
>       06:00:00",
>       "2012-02-02 12:00:00", "2012-02-02 18:00:00", "2012-02-03
>       00:00:00",
>       "2012-02-03 06:00:00", "2012-02-03 12:00:00", "2012-02-03
>       18:00:00",
>       "2012-02-04 00:00:00", "2012-02-04 06:00:00", "2012-02-04
>       12:00:00",
>       "2012-02-04 18:00:00", "2012-02-05 00:00:00", "2012-02-05
>       06:00:00",
>       "2012-02-05 12:00:00", "2012-02-05 18:00:00", "2012-02-06
>       00:00:00",
>       "2012-02-06 06:00:00", "2012-02-06 12:00:00", "2012-02-06
>       18:00:00",
>       "2012-02-07 00:00:00", "2012-02-07 06:00:00", "2012-02-07
>       12:00:00",
>       "2012-02-07 18:00:00", "2012-02-08 00:00:00", "2012-02-08
>       06:00:00",
>       "2012-02-08 12:00:00", "2012-02-08 18:00:00", "2012-02-09
>       00:00:00",
>       "2012-02-09 06:00:00", "2012-02-09 12:00:00", "2012-02-09
>       18:00:00",
>       "2012-02-10 00:00:00", "2012-02-10 06:00:00", "2012-02-10
>       12:00:00",
>       "2012-02-10 18:00:00", "2012-02-11 00:00:00", "2012-02-11
>       06:00:00",
>       "2012-02-11 12:00:00", "2012-02-11 18:00:00", "2012-02-12
>       00:00:00",
>       "2012-02-12 06:00:00", "2012-02-12 12:00:00", "2012-02-12
>       18:00:00",
>       "2012-02-13 00:00:00", "2012-02-13 06:00:00", "2012-02-13
>       12:00:00",
>       "2012-02-13 18:00:00", "2012-02-14 00:00:00", "2012-02-14
>       06:00:00",
>       "2012-02-14 12:00:00", "2012-02-14 18:00:00", "2012-02-15
>       00:00:00",
>       "2012-02-15 06:00:00", "2012-02-15 12:00:00", "2012-02-15
>       18:00:00",
>       "2012-02-16 00:00:00", "2012-02-16 06:00:00", "2012-02-16
>       12:00:00",
>       "2012-02-16 18:00:00", "2012-02-17 00:00:00", "2012-02-17
>       06:00:00",
>       "2012-02-17 12:00:00", "2012-02-17 18:00:00", "2012-02-18
>       00:00:00",
>       "2012-02-18 06:00:00", "2012-02-18 12:00:00", "2012-02-18
>       18:00:00",
>       "2012-02-19 00:00:00", "2012-02-19 06:00:00", "2012-02-19
>       12:00:00",
>       "2012-02-19 18:00:00", "2012-02-20 00:00:00", "2012-02-20
>       06:00:00",
>       "2012-02-20 12:00:00", "2012-02-20 18:00:00", "2012-02-21
>       00:00:00",
>       "2012-02-21 06:00:00", "2012-02-21 12:00:00", "2012-02-21
>       18:00:00",
>       "2012-02-22 00:00:00", "2012-02-22 06:00:00", "2012-02-22
>       12:00:00",
>       "2012-02-22 18:00:00", "2012-02-23 00:00:00", "2012-02-23
>       06:00:00",
>       "2012-02-23 12:00:00", "2012-02-23 18:00:00", "2012-02-24
>       00:00:00",
>       "2012-02-24 06:00:00", "2012-02-24 12:00:00", "2012-02-24
>       18:00:00",
>       "2012-02-25 00:00:00", "2012-02-25 06:00:00", "2012-02-25
>       12:00:00",
>       "2012-02-25 18:00:00", "2012-02-26 00:00:00", "2012-02-26
>       06:00:00",
>       "2012-02-26 12:00:00", "2012-02-26 18:00:00", "2012-02-27
>       00:00:00",
>       "2012-02-27 06:00:00", "2012-02-27 12:00:00", "2012-02-27
>       18:00:00",
>       "2012-02-28 00:00:00", "2012-02-28 06:00:00", "2012-02-28
>       12:00:00",
>       "2012-02-28 18:00:00", "2012-02-29 00:00:00", "2012-02-29
>       06:00:00",
>       "2012-02-29 12:00:00", "2012-02-29 18:00:00", "2012-03-01
>       00:00:00",
>       "2012-03-01 06:00:00", "2012-03-01 12:00:00", "2012-03-01
>       18:00:00",
>       "2012-03-02 00:00:00", "2012-03-02 06:00:00", "2012-03-02
>       12:00:00",
>       "2012-03-02 18:00:00", "2012-03-03 00:00:00", "2012-03-03
>       06:00:00",
>       "2012-03-03 12:00:00", "2012-03-03 18:00:00", "2012-03-04
>       00:00:00",
>       "2012-03-04 06:00:00", "2012-03-04 12:00:00", "2012-03-04
>       18:00:00",
>       "2012-03-05 00:00:00", "2012-03-05 06:00:00", "2012-03-05
>       12:00:00",
>       "2012-03-05 18:00:00", "2012-03-06 00:00:00", "2012-03-06
>       06:00:00",
>       "2012-03-06 12:00:00", "2012-03-06 18:00:00", "2012-03-07
>       00:00:00",
>       "2012-03-07 06:00:00", "2012-03-07 12:00:00", "2012-03-07
>       18:00:00",
>       "2012-03-08 00:00:00", "2012-03-08 06:00:00", "2012-03-08
>       12:00:00",
>       "2012-03-08 18:00:00", "2012-03-09 00:00:00", "2012-03-09
>       06:00:00",
>       "2012-03-09 12:00:00", "2012-03-09 18:00:00", "2012-03-10
>       00:00:00",
>       "2012-03-10 06:00:00", "2012-03-10 12:00:00", "2012-03-10
>       18:00:00",
>       "2012-03-11 00:00:00", "2012-03-11 06:00:00", "2012-03-11
>       12:00:00",
>       "2012-03-11 18:00:00", "2012-03-12 00:00:00", "2012-03-12
>       06:00:00",
>       "2012-03-12 12:00:00", "2012-03-12 18:00:00", "2012-03-13
>       00:00:00",
>       "2012-03-13 06:00:00", "2012-03-13 12:00:00", "2012-03-13
>       18:00:00",
>       "2012-03-14 00:00:00", "2012-03-14 06:00:00", "2012-03-14
>       12:00:00",
>       "2012-03-14 18:00:00", "2012-03-15 00:00:00", "2012-03-15
>       06:00:00",
>       "2012-03-15 12:00:00", "2012-03-15 18:00:00", "2012-03-16
>       00:00:00",
>       "2012-03-16 06:00:00", "2012-03-16 12:00:00", "2012-03-16
>       18:00:00",
>       "2012-03-17 00:00:00", "2012-03-17 06:00:00", "2012-03-17
>       12:00:00",
>       "2012-03-17 18:00:00", "2012-03-18 00:00:00", "2012-03-18
>       06:00:00",
>       "2012-03-18 12:00:00", "2012-03-18 18:00:00", "2012-03-19
>       00:00:00",
>       "2012-03-19 06:00:00", "2012-03-19 12:00:00", "2012-03-19
>       18:00:00",
>       "2012-03-20 00:00:00", "2012-03-20 06:00:00", "2012-03-20
>       12:00:00",
>       "2012-03-20 18:00:00", "2012-03-21 00:00:00", "2012-03-21
>       06:00:00",
>       "2012-03-21 12:00:00", "2012-03-21 18:00:00", "2012-03-22
>       00:00:00",
>       "2012-03-22 06:00:00", "2012-03-22 12:00:00", "2012-03-22
>       18:00:00",
>       "2012-03-23 00:00:00", "2012-03-23 06:00:00", "2012-03-23
>       12:00:00",
>       "2012-03-23 18:00:00", "2012-03-24 00:00:00", "2012-03-24
>       06:00:00",
>       "2012-03-24 12:00:00", "2012-03-24 18:00:00", "2012-03-25
>       00:00:00",
>       "2012-03-25 06:00:00", "2012-03-25 12:00:00", "2012-03-25
>       18:00:00",
>       "2012-03-26 00:00:00", "2012-03-26 06:00:00", "2012-03-26
>       12:00:00",
>       "2012-03-26 18:00:00", "2012-03-27 00:00:00", "2012-03-27
>       06:00:00",
>       "2012-03-27 12:00:00", "2012-03-27 18:00:00", "2012-03-28
>       00:00:00",
>       "2012-03-28 06:00:00", "2012-03-28 12:00:00", "2012-03-28
>       18:00:00",
>       "2012-03-29 00:00:00", "2012-03-29 06:00:00", "2012-03-29
>       12:00:00",
>       "2012-03-29 18:00:00", "2012-03-30 00:00:00", "2012-03-30
>       06:00:00",
>       "2012-03-30 12:00:00", "2012-03-30 18:00:00", "2012-03-31
>       00:00:00",
>       "2012-03-31 06:00:00", "2012-03-31 12:00:00", "2012-03-31
>       18:00:00",
>       "2012-04-01 00:00:00", "2012-04-01 06:00:00", "2012-04-01
>       12:00:00",
>       "2012-04-01 18:00:00", "2012-04-02 00:00:00", "2012-04-02
>       06:00:00",
>       "2012-04-02 12:00:00", "2012-04-02 18:00:00", "2012-04-03
>       00:00:00",
>       "2012-04-03 06:00:00", "2012-04-03 12:00:00", "2012-04-03
>       18:00:00",
>       "2012-04-04 00:00:00", "2012-04-04 06:00:00", "2012-04-04
>       12:00:00",
>       "2012-04-04 18:00:00", "2012-04-05 00:00:00", "2012-04-05
>       06:00:00",
>       "2012-04-05 12:00:00", "2012-04-05 18:00:00", "2012-04-06
>       00:00:00",
>       "2012-04-06 06:00:00", "2012-04-06 12:00:00", "2012-04-06
>       18:00:00",
>       "2012-04-07 00:00:00", "2012-04-07 06:00:00", "2012-04-07
>       12:00:00",
>       "2012-04-07 18:00:00", "2012-04-08 00:00:00", "2012-04-08
>       06:00:00",
>       "2012-04-08 12:00:00", "2012-04-08 18:00:00", "2012-04-09
>       00:00:00",
>       "2012-04-09 06:00:00", "2012-04-09 12:00:00", "2012-04-09
>       18:00:00",
>       "2012-04-10 00:00:00", "2012-04-10 06:00:00", "2012-04-10
>       12:00:00",
>       "2012-04-10 18:00:00", "2012-04-11 00:00:00", "2012-04-11
>       06:00:00",
>       "2012-04-11 12:00:00", "2012-04-11 18:00:00", "2012-04-12
>       00:00:00",
>       "2012-04-12 06:00:00", "2012-04-12 12:00:00", "2012-04-12
>       18:00:00",
>       "2012-04-13 00:00:00", "2012-04-13 06:00:00", "2012-04-13
>       12:00:00",
>       "2012-04-13 18:00:00", "2012-04-14 00:00:00", "2012-04-14
>       06:00:00",
>       "2012-04-14 12:00:00", "2012-04-14 18:00:00", "2012-04-15
>       00:00:00",
>       "2012-04-15 06:00:00", "2012-04-15 12:00:00", "2012-04-15
>       18:00:00",
>       "2012-04-16 00:00:00", "2012-04-16 06:00:00", "2012-04-16
>       12:00:00",
>       "2012-04-16 18:00:00", "2012-04-17 00:00:00", "2012-04-17
>       06:00:00",
>       "2012-04-17 12:00:00", "2012-04-17 18:00:00", "2012-04-18
>       00:00:00",
>       "2012-04-18 06:00:00", "2012-04-18 12:00:00", "2012-04-18
>       18:00:00",
>       "2012-04-19 00:00:00", "2012-04-19 06:00:00", "2012-04-19
>       12:00:00",
>       "2012-04-19 18:00:00", "2012-04-20 00:00:00", "2012-04-20
>       06:00:00",
>       "2012-04-20 12:00:00", "2012-04-20 18:00:00", "2012-04-21
>       00:00:00",
>       "2012-04-21 06:00:00", "2012-04-21 12:00:00", "2012-04-21
>       18:00:00",
>       "2012-04-22 00:00:00", "2012-04-22 06:00:00", "2012-04-22
>       12:00:00",
>       "2012-04-22 18:00:00", "2012-04-23 00:00:00", "2012-04-23
>       06:00:00",
>       "2012-04-23 12:00:00", "2012-04-23 18:00:00", "2012-04-24
>       00:00:00",
>       "2012-04-24 06:00:00", "2012-04-24 12:00:00", "2012-04-24
>       18:00:00",
>       "2012-04-25 00:00:00", "2012-04-25 06:00:00", "2012-04-25
>       12:00:00",
>       "2012-04-25 18:00:00", "2012-04-26 00:00:00", "2012-04-26
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>       "2012-04-26 12:00:00", "2012-04-26 18:00:00", "2012-04-27
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>       "2012-04-27 06:00:00", "2012-04-27 12:00:00", "2012-04-27
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>       "2012-04-28 00:00:00", "2012-04-28 06:00:00", "2012-04-28
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>       "2012-04-28 18:00:00", "2012-04-29 00:00:00", "2012-04-29
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>       "2012-04-29 12:00:00", "2012-04-29 18:00:00", "2012-04-30
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>       "2012-04-30 06:00:00", "2012-04-30 12:00:00", "2012-04-30
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>       "2012-05-03 06:00:00", "2012-05-03 12:00:00", "2012-05-03
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>       "2012-05-04 00:00:00", "2012-05-04 06:00:00", "2012-05-04
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>       "2012-05-07 18:00:00", "2012-05-08 00:00:00", "2012-05-08
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>       "2012-05-08 12:00:00", "2012-05-08 18:00:00", "2012-05-09
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>       "2012-05-09 06:00:00", "2012-05-09 12:00:00", "2012-05-09
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>       "2012-05-10 00:00:00", "2012-05-10 06:00:00", "2012-05-10
>       12:00:00",
>       "2012-05-10 18:00:00", "2012-05-11 00:00:00", "2012-05-11
>       06:00:00",
>       "2012-05-11 12:00:00", "2012-05-11 18:00:00", "2012-05-12
>       00:00:00",
>       "2012-05-12 06:00:00", "2012-05-12 12:00:00", "2012-05-12
>       18:00:00",
>       "2012-05-13 00:00:00", "2012-05-13 06:00:00", "2012-05-13
>       12:00:00",
>       "2012-05-13 18:00:00", "2012-05-14 00:00:00", "2012-05-14
>       06:00:00",
>       "2012-05-14 12:00:00", "2012-05-14 18:00:00", "2012-05-15
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>       "2012-05-15 06:00:00", "2012-05-15 12:00:00", "2012-05-15
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>       "2012-05-16 00:00:00", "2012-05-16 06:00:00", "2012-05-16
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>       "2012-05-16 18:00:00", "2012-05-17 00:00:00", "2012-05-17
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>       "2012-05-17 12:00:00", "2012-05-17 18:00:00", "2012-05-18
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>       "2012-05-18 06:00:00", "2012-05-18 12:00:00", "2012-05-18
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>       "2012-05-19 00:00:00", "2012-05-19 06:00:00", "2012-05-19
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>       "2012-05-19 18:00:00", "2012-05-20 00:00:00", "2012-05-20
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>       "2012-05-20 12:00:00", "2012-05-20 18:00:00", "2012-05-21
>       00:00:00",
>       "2012-05-21 06:00:00", "2012-05-21 12:00:00", "2012-05-21
>       18:00:00",
>       "2012-05-22 00:00:00", "2012-05-22 06:00:00", "2012-05-22
>       12:00:00",
>       "2012-05-22 18:00:00", "2012-05-23 00:00:00", "2012-05-23
>       06:00:00",
>       "2012-05-23 12:00:00", "2012-05-23 18:00:00", "2012-05-24
>       00:00:00",
>       "2012-05-24 06:00:00", "2012-05-24 12:00:00", "2012-05-24
>       18:00:00",
>       "2012-05-25 00:00:00", "2012-05-25 06:00:00", "2012-05-25
>       12:00:00",
>       "2012-05-25 18:00:00", "2012-05-26 00:00:00", "2012-05-26
>       06:00:00",
>       "2012-05-26 12:00:00", "2012-05-26 18:00:00", "2012-05-27
>       00:00:00",
>       "2012-05-27 06:00:00", "2012-05-27 12:00:00", "2012-05-27
>       18:00:00",
>       "2012-05-28 00:00:00", "2012-05-28 06:00:00", "2012-05-28
>       12:00:00",
>       "2012-05-28 18:00:00", "2012-05-29 00:00:00", "2012-05-29
>       06:00:00",
>       "2012-05-29 12:00:00"), class = "factor"), basistime =
>       structure(c(1L,
>       1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
>       1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
>       2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L,
>       3L), .Label = c("2012-01-25 15:02:00", "2012-01-26 15:11:00",
>       "2012-01-27 01:41:00", "2012-01-27 10:15:00", "2012-01-27
>       15:15:00",
>       "2012-01-28 14:22:00", "2012-01-29 13:33:00", "2012-01-30
>       14:11:00",
>       "2012-01-31 14:24:00", "2012-02-01 14:55:00", "2012-02-02
>       14:56:00",
>       "2012-02-03 14:40:00", "2012-02-04 15:01:00", "2012-02-05
>       15:04:00",
>       "2012-02-06 14:37:00", "2012-02-07 14:42:00", "2012-02-08
>       14:44:00",
>       "2012-02-09 14:27:00", "2012-02-10 14:33:00", "2012-02-11
>       15:05:00",
>       "2012-02-12 15:09:00", "2012-02-13 15:00:00", "2012-02-14
>       15:10:00",
>       "2012-02-15 14:46:00", "2012-02-16 14:42:00", "2012-02-17
>       14:14:00",
>       "2012-02-18 15:27:00", "2012-02-19 13:13:00", "2012-02-20
>       13:56:00",
>       "2012-02-21 14:39:00", "2012-02-22 15:33:00", "2012-02-23
>       15:14:00",
>       "2012-02-24 15:14:00", "2012-02-25 14:25:00", "2012-02-26
>       14:08:00",
>       "2012-02-27 14:55:00", "2012-02-28 14:40:00", "2012-02-29
>       14:45:00",
>       "2012-03-01 15:18:00", "2012-03-02 15:18:00", "2012-03-03
>       15:43:00",
>       "2012-03-04 15:16:00", "2012-03-05 15:17:00", "2012-03-06
>       15:03:00",
>       "2012-03-07 14:44:00", "2012-03-08 14:53:00", "2012-03-09
>       15:10:00",
>       "2012-03-10 14:43:00", "2012-03-11 13:37:00", "2012-03-12
>       14:58:00",
>       "2012-03-13 14:36:00", "2012-03-14 13:49:00", "2012-03-15
>       14:32:00",
>       "2012-03-16 15:01:00", "2012-03-17 13:55:00", "2012-03-18
>       13:44:00",
>       "2012-03-19 13:55:00", "2012-03-20 13:53:00", "2012-03-21
>       14:07:00",
>       "2012-03-22 14:03:00", "2012-03-23 14:30:00", "2012-03-24
>       14:47:00",
>       "2012-03-25 14:32:00", "2012-03-26 14:41:00", "2012-03-27
>       13:51:00",
>       "2012-03-28 13:32:00", "2012-03-29 13:59:00", "2012-03-30
>       14:15:00",
>       "2012-03-31 14:12:00", "2012-04-01 14:30:00", "2012-04-02
>       13:43:00",
>       "2012-04-03 13:54:00", "2012-04-04 13:45:00", "2012-04-05
>       13:46:00",
>       "2012-04-06 13:41:00", "2012-04-07 13:13:00", "2012-04-08
>       12:59:00",
>       "2012-04-09 13:53:00", "2012-04-10 14:15:00", "2012-04-11
>       14:26:00",
>       "2012-04-12 14:05:00", "2012-04-13 13:37:00", "2012-04-14
>       13:52:00",
>       "2012-04-15 15:00:00", "2012-04-16 14:42:00", "2012-04-17
>       14:21:00",
>       "2012-04-18 14:40:00", "2012-04-19 14:35:00", "2012-04-20
>       15:14:00",
>       "2012-04-21 14:46:00", "2012-04-22 14:44:00", "2012-04-23
>       14:33:00",
>       "2012-04-24 14:41:00", "2012-04-25 14:13:00", "2012-04-26
>       14:19:00",
>       "2012-04-27 14:35:00", "2012-04-28 13:48:00", "2012-04-29
>       14:12:00",
>       "2012-04-30 13:53:00", "2012-05-02 14:41:00", "2012-05-03
>       15:01:00",
>       "2012-05-04 15:21:00", "2012-05-05 14:57:00", "2012-05-06
>       14:09:00",
>       "2012-05-07 14:30:00", "2012-05-08 14:05:00", "2012-05-08
>       21:21:00",
>       "2012-05-09 15:02:00", "2012-05-10 14:27:00", "2012-05-11
>       14:47:00",
>       "2012-05-12 13:24:00", "2012-05-13 14:40:00", "2012-05-13
>       19:24:00",
>       "2012-05-14 14:33:00", "2012-05-15 14:39:00", "2012-05-16
>       14:07:00",
>       "2012-05-17 13:42:00", "2012-05-18 14:30:00", "2012-05-19
>       13:59:00",
>       "2012-05-20 14:14:00", "2012-05-21 14:15:00", "2012-05-22
>       14:18:00",
>       "2012-05-23 14:14:00", "2012-05-24 13:52:00"), class =
>       "factor"),
>           fcst = c(38.7, 38.9, 39.2, 39.8, 40.5, 41.5, 42.5, 43.1,
>           43.9, 44.5, 44.8, 45, 45, 45.1, 45.4, 45.8, 46.4, 47, 47.5,
>           47.9, 39.2, 40, 41.8, 42.2, 42.8, 44.4, 45.7, 46.2, 46.2,
>           46.2, 46.5, 47, 47.5, 47.9, 48.4, 49, 49.5, 49.9, 50.2,
>       50.4,
>           41.3, 42.5, 42.8, 42.8, 42.8, 42.9, 43, 43.3, 43.5, 43.8),
>           usgs = c(38.5, 38.6, 38.6, 38.6, 39.1, 39.8, 41.2, 42.9,
>           43.4, 43.6, 43.4, 43.1, 43, 43.1, 43.5, 43.8, 44.1, 44.2,
>           44.4, 44.5, 39.1, 39.8, 41.2, 42.9, 43.4, 43.6, 43.4, 43.1,
>           43, 43.1, 43.5, 43.8, 44.1, 44.2, 44.4, 44.5, 44.5, 44.5,
>           44.6, 44.2, 41.2, 42.9, 43.4, 43.6, 43.4, 43.1, 43, 43.1,
>           43.5, 43.8)), .Names = c("date", "basistime", "fcst", "usgs"
>       ), row.names = c(NA, 50L), class = "data.frame")
> 
> Sys.setenv( "Etc/GMT+8" ) # or whatever is appropriate
> #> Error in Sys.setenv("Etc/GMT+8"): all arguments must be named
> 
> dta2 <- dta
> # bad idea to work with dates as factors
> dta2$date <- as.POSIXct( as.character( dta2$date ) )
> dta2$basistime <- as.POSIXct( as.character( dta2$basistime ) )
> 
> # base R solution
> 
> dates <- unique( dta2$date )
> dta2list <- split( dta2, dta2$date )
> grplist <- lapply( dta2list
>                  , function( DF ) {
>                      DF[ which.max( DF$fcst ), ]
>                    }
>                  )
> result2 <- do.call( rbind, grplist )
> result2
> #>                                    date           basistime fcst
> usgs
> #> 2012-01-25 18:00:00 2012-01-25 18:00:00 2012-01-25 15:02:00 38.7
> 38.5
> #> 2012-01-26 00:00:00 2012-01-26 00:00:00 2012-01-25 15:02:00 38.9
> 38.6
> #> 2012-01-26 06:00:00 2012-01-26 06:00:00 2012-01-25 15:02:00 39.2
> 38.6
> #> 2012-01-26 12:00:00 2012-01-26 12:00:00 2012-01-25 15:02:00 39.8
> 38.6
> #> 2012-01-26 18:00:00 2012-01-26 18:00:00 2012-01-25 15:02:00 40.5
> 39.1
> #> 2012-01-27 00:00:00 2012-01-27 00:00:00 2012-01-25 15:02:00 41.5
> 39.8
> #> 2012-01-27 06:00:00 2012-01-27 06:00:00 2012-01-25 15:02:00 42.5
> 41.2
> #> 2012-01-27 12:00:00 2012-01-27 12:00:00 2012-01-25 15:02:00 43.1
> 42.9
> #> 2012-01-27 18:00:00 2012-01-27 18:00:00 2012-01-25 15:02:00 43.9
> 43.4
> #> 2012-01-28 00:00:00 2012-01-28 00:00:00 2012-01-25 15:02:00 44.5
> 43.6
> #> 2012-01-28 06:00:00 2012-01-28 06:00:00 2012-01-26 15:11:00 45.7
> 43.4
> #> 2012-01-28 12:00:00 2012-01-28 12:00:00 2012-01-26 15:11:00 46.2
> 43.1
> #> 2012-01-28 18:00:00 2012-01-28 18:00:00 2012-01-26 15:11:00 46.2
> 43.0
> #> 2012-01-29 00:00:00 2012-01-29 00:00:00 2012-01-26 15:11:00 46.2
> 43.1
> #> 2012-01-29 06:00:00 2012-01-29 06:00:00 2012-01-26 15:11:00 46.5
> 43.5
> #> 2012-01-29 12:00:00 2012-01-29 12:00:00 2012-01-26 15:11:00 47.0
> 43.8
> #> 2012-01-29 18:00:00 2012-01-29 18:00:00 2012-01-26 15:11:00 47.5
> 44.1
> #> 2012-01-30 00:00:00 2012-01-30 00:00:00 2012-01-26 15:11:00 47.9
> 44.2
> #> 2012-01-30 06:00:00 2012-01-30 06:00:00 2012-01-26 15:11:00 48.4
> 44.4
> #> 2012-01-30 12:00:00 2012-01-30 12:00:00 2012-01-26 15:11:00 49.0
> 44.5
> #> 2012-01-30 18:00:00 2012-01-30 18:00:00 2012-01-26 15:11:00 49.5
> 44.5
> #> 2012-01-31 00:00:00 2012-01-31 00:00:00 2012-01-26 15:11:00 49.9
> 44.5
> #> 2012-01-31 06:00:00 2012-01-31 06:00:00 2012-01-26 15:11:00 50.2
> 44.6
> #> 2012-01-31 12:00:00 2012-01-31 12:00:00 2012-01-26 15:11:00 50.4
> 44.2
> 
> # alternately, use tidyverse
> 
> library(dplyr)
> #>
> #> Attaching package: 'dplyr'
> #> The following objects are masked from 'package:stats':
> #>
> #>     filter, lag
> #> The following objects are masked from 'package:base':
> #>
> #>     intersect, setdiff, setequal, union
> result3 <- (   dta2
>            %>% group_by( date )
>            %>% do({
>                  DF <- .
>                  DF[ which.max( DF$fcst ), ]
>                })
>            %>% ungroup
>            %>% as.data.frame
>            )
> result3
> #>                   date           basistime fcst usgs
> #> 1  2012-01-25 18:00:00 2012-01-25 15:02:00 38.7 38.5
> #> 2  2012-01-26 00:00:00 2012-01-25 15:02:00 38.9 38.6
> #> 3  2012-01-26 06:00:00 2012-01-25 15:02:00 39.2 38.6
> #> 4  2012-01-26 12:00:00 2012-01-25 15:02:00 39.8 38.6
> #> 5  2012-01-26 18:00:00 2012-01-25 15:02:00 40.5 39.1
> #> 6  2012-01-27 00:00:00 2012-01-25 15:02:00 41.5 39.8
> #> 7  2012-01-27 06:00:00 2012-01-25 15:02:00 42.5 41.2
> #> 8  2012-01-27 12:00:00 2012-01-25 15:02:00 43.1 42.9
> #> 9  2012-01-27 18:00:00 2012-01-25 15:02:00 43.9 43.4
> #> 10 2012-01-28 00:00:00 2012-01-25 15:02:00 44.5 43.6
> #> 11 2012-01-28 06:00:00 2012-01-26 15:11:00 45.7 43.4
> #> 12 2012-01-28 12:00:00 2012-01-26 15:11:00 46.2 43.1
> #> 13 2012-01-28 18:00:00 2012-01-26 15:11:00 46.2 43.0
> #> 14 2012-01-29 00:00:00 2012-01-26 15:11:00 46.2 43.1
> #> 15 2012-01-29 06:00:00 2012-01-26 15:11:00 46.5 43.5
> #> 16 2012-01-29 12:00:00 2012-01-26 15:11:00 47.0 43.8
> #> 17 2012-01-29 18:00:00 2012-01-26 15:11:00 47.5 44.1
> #> 18 2012-01-30 00:00:00 2012-01-26 15:11:00 47.9 44.2
> #> 19 2012-01-30 06:00:00 2012-01-26 15:11:00 48.4 44.4
> #> 20 2012-01-30 12:00:00 2012-01-26 15:11:00 49.0 44.5
> #> 21 2012-01-30 18:00:00 2012-01-26 15:11:00 49.5 44.5
> #> 22 2012-01-31 00:00:00 2012-01-26 15:11:00 49.9 44.5
> #> 23 2012-01-31 06:00:00 2012-01-26 15:11:00 50.2 44.6
> #> 24 2012-01-31 12:00:00 2012-01-26 15:11:00 50.4 44.2
> 
> ####################################################
> 
> 
> On Thu, 26 Oct 2017, Thomas Adams wrote:
>
>       Hello all!
>
>       I've been struggling with is for many hours today; I'm
>       close to getting
>       what I want, but not close enough...
>
>       I have a dataframe consisting of two date-time columns
>       followed by two
>       numeric columns. what I need is the max value (in the
>       first numeric column)
>       based on the 2nd date-time column, which is essentially a
>       factor. But, I
>       want the result to provide both date-time values
>       corresponding to the max
>       value.
>
>       My data:
>
>       structure(list(date = structure(c(1L, 2L, 3L, 4L, 5L, 6L,
>       7L,
>       8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L, 19L,
>       20L,
>       5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L,
>       17L, 18L,
>       19L, 20L, 21L, 22L, 23L, 24L, 7L, 8L, 9L, 10L, 11L, 12L,
>       13L,
>       14L, 15L, 16L), .Label = c("2012-01-25 18:00:00",
>       "2012-01-26 00:00:00",
>       "2012-01-26 06:00:00", "2012-01-26 12:00:00", "2012-01-26
>       18:00:00",
>       "2012-01-27 00:00:00", "2012-01-27 06:00:00", "2012-01-27
>       12:00:00",
>       "2012-01-27 18:00:00", "2012-01-28 00:00:00", "2012-01-28
>       06:00:00",
>       "2012-01-28 12:00:00", "2012-01-28 18:00:00", "2012-01-29
>       00:00:00",
>       "2012-01-29 06:00:00", "2012-01-29 12:00:00", "2012-01-29
>       18:00:00",
>       "2012-01-30 00:00:00", "2012-01-30 06:00:00", "2012-01-30
>       12:00:00",
>       "2012-01-30 18:00:00", "2012-01-31 00:00:00", "2012-01-31
>       06:00:00",
>       "2012-01-31 12:00:00", "2012-01-31 13:00:00", "2012-01-31
>       18:00:00",
>       "2012-02-01 00:00:00", "2012-02-01 06:00:00", "2012-02-01
>       12:00:00",
>       "2012-02-01 18:00:00", "2012-02-02 00:00:00", "2012-02-02
>       06:00:00",
>       "2012-02-02 12:00:00", "2012-02-02 18:00:00", "2012-02-03
>       00:00:00",
>       "2012-02-03 06:00:00", "2012-02-03 12:00:00", "2012-02-03
>       18:00:00",
>       "2012-02-04 00:00:00", "2012-02-04 06:00:00", "2012-02-04
>       12:00:00",
>       "2012-02-04 18:00:00", "2012-02-05 00:00:00", "2012-02-05
>       06:00:00",
>       "2012-02-05 12:00:00", "2012-02-05 18:00:00", "2012-02-06
>       00:00:00",
>       "2012-02-06 06:00:00", "2012-02-06 12:00:00", "2012-02-06
>       18:00:00",
>       "2012-02-07 00:00:00", "2012-02-07 06:00:00", "2012-02-07
>       12:00:00",
>       "2012-02-07 18:00:00", "2012-02-08 00:00:00", "2012-02-08
>       06:00:00",
>       "2012-02-08 12:00:00", "2012-02-08 18:00:00", "2012-02-09
>       00:00:00",
>       "2012-02-09 06:00:00", "2012-02-09 12:00:00", "2012-02-09
>       18:00:00",
>       "2012-02-10 00:00:00", "2012-02-10 06:00:00", "2012-02-10
>       12:00:00",
>       "2012-02-10 18:00:00", "2012-02-11 00:00:00", "2012-02-11
>       06:00:00",
>       "2012-02-11 12:00:00", "2012-02-11 18:00:00", "2012-02-12
>       00:00:00",
>       "2012-02-12 06:00:00", "2012-02-12 12:00:00", "2012-02-12
>       18:00:00",
>       "2012-02-13 00:00:00", "2012-02-13 06:00:00", "2012-02-13
>       12:00:00",
>       "2012-02-13 18:00:00", "2012-02-14 00:00:00", "2012-02-14
>       06:00:00",
>       "2012-02-14 12:00:00", "2012-02-14 18:00:00", "2012-02-15
>       00:00:00",
>       "2012-02-15 06:00:00", "2012-02-15 12:00:00", "2012-02-15
>       18:00:00",
>       "2012-02-16 00:00:00", "2012-02-16 06:00:00", "2012-02-16
>       12:00:00",
>       "2012-02-16 18:00:00", "2012-02-17 00:00:00", "2012-02-17
>       06:00:00",
>       "2012-02-17 12:00:00", "2012-02-17 18:00:00", "2012-02-18
>       00:00:00",
>       "2012-02-18 06:00:00", "2012-02-18 12:00:00", "2012-02-18
>       18:00:00",
>       "2012-02-19 00:00:00", "2012-02-19 06:00:00", "2012-02-19
>       12:00:00",
>       "2012-02-19 18:00:00", "2012-02-20 00:00:00", "2012-02-20
>       06:00:00",
>       "2012-02-20 12:00:00", "2012-02-20 18:00:00", "2012-02-21
>       00:00:00",
>       "2012-02-21 06:00:00", "2012-02-21 12:00:00", "2012-02-21
>       18:00:00",
>       "2012-02-22 00:00:00", "2012-02-22 06:00:00", "2012-02-22
>       12:00:00",
>       "2012-02-22 18:00:00", "2012-02-23 00:00:00", "2012-02-23
>       06:00:00",
>       "2012-02-23 12:00:00", "2012-02-23 18:00:00", "2012-02-24
>       00:00:00",
>       "2012-02-24 06:00:00", "2012-02-24 12:00:00", "2012-02-24
>       18:00:00",
>       "2012-02-25 00:00:00", "2012-02-25 06:00:00", "2012-02-25
>       12:00:00",
>       "2012-02-25 18:00:00", "2012-02-26 00:00:00", "2012-02-26
>       06:00:00",
>       "2012-02-26 12:00:00", "2012-02-26 18:00:00", "2012-02-27
>       00:00:00",
>       "2012-02-27 06:00:00", "2012-02-27 12:00:00", "2012-02-27
>       18:00:00",
>       "2012-02-28 00:00:00", "2012-02-28 06:00:00", "2012-02-28
>       12:00:00",
>       "2012-02-28 18:00:00", "2012-02-29 00:00:00", "2012-02-29
>       06:00:00",
>       "2012-02-29 12:00:00", "2012-02-29 18:00:00", "2012-03-01
>       00:00:00",
>       "2012-03-01 06:00:00", "2012-03-01 12:00:00", "2012-03-01
>       18:00:00",
>       "2012-03-02 00:00:00", "2012-03-02 06:00:00", "2012-03-02
>       12:00:00",
>       "2012-03-02 18:00:00", "2012-03-03 00:00:00", "2012-03-03
>       06:00:00",
>       "2012-03-03 12:00:00", "2012-03-03 18:00:00", "2012-03-04
>       00:00:00",
>       "2012-03-04 06:00:00", "2012-03-04 12:00:00", "2012-03-04
>       18:00:00",
>       "2012-03-05 00:00:00", "2012-03-05 06:00:00", "2012-03-05
>       12:00:00",
>       "2012-03-05 18:00:00", "2012-03-06 00:00:00", "2012-03-06
>       06:00:00",
>       "2012-03-06 12:00:00", "2012-03-06 18:00:00", "2012-03-07
>       00:00:00",
>       "2012-03-07 06:00:00", "2012-03-07 12:00:00", "2012-03-07
>       18:00:00",
>       "2012-03-08 00:00:00", "2012-03-08 06:00:00", "2012-03-08
>       12:00:00",
>       "2012-03-08 18:00:00", "2012-03-09 00:00:00", "2012-03-09
>       06:00:00",
>       "2012-03-09 12:00:00", "2012-03-09 18:00:00", "2012-03-10
>       00:00:00",
>       "2012-03-10 06:00:00", "2012-03-10 12:00:00", "2012-03-10
>       18:00:00",
>       "2012-03-11 00:00:00", "2012-03-11 06:00:00", "2012-03-11
>       12:00:00",
>       "2012-03-11 18:00:00", "2012-03-12 00:00:00", "2012-03-12
>       06:00:00",
>       "2012-03-12 12:00:00", "2012-03-12 18:00:00", "2012-03-13
>       00:00:00",
>       "2012-03-13 06:00:00", "2012-03-13 12:00:00", "2012-03-13
>       18:00:00",
>       "2012-03-14 00:00:00", "2012-03-14 06:00:00", "2012-03-14
>       12:00:00",
>       "2012-03-14 18:00:00", "2012-03-15 00:00:00", "2012-03-15
>       06:00:00",
>       "2012-03-15 12:00:00", "2012-03-15 18:00:00", "2012-03-16
>       00:00:00",
>       "2012-03-16 06:00:00", "2012-03-16 12:00:00", "2012-03-16
>       18:00:00",
>       "2012-03-17 00:00:00", "2012-03-17 06:00:00", "2012-03-17
>       12:00:00",
>       "2012-03-17 18:00:00", "2012-03-18 00:00:00", "2012-03-18
>       06:00:00",
>       "2012-03-18 12:00:00", "2012-03-18 18:00:00", "2012-03-19
>       00:00:00",
>       "2012-03-19 06:00:00", "2012-03-19 12:00:00", "2012-03-19
>       18:00:00",
>       "2012-03-20 00:00:00", "2012-03-20 06:00:00", "2012-03-20
>       12:00:00",
>       "2012-03-20 18:00:00", "2012-03-21 00:00:00", "2012-03-21
>       06:00:00",
>       "2012-03-21 12:00:00", "2012-03-21 18:00:00", "2012-03-22
>       00:00:00",
>       "2012-03-22 06:00:00", "2012-03-22 12:00:00", "2012-03-22
>       18:00:00",
>       "2012-03-23 00:00:00", "2012-03-23 06:00:00", "2012-03-23
>       12:00:00",
>       "2012-03-23 18:00:00", "2012-03-24 00:00:00", "2012-03-24
>       06:00:00",
>       "2012-03-24 12:00:00", "2012-03-24 18:00:00", "2012-03-25
>       00:00:00",
>       "2012-03-25 06:00:00", "2012-03-25 12:00:00", "2012-03-25
>       18:00:00",
>       "2012-03-26 00:00:00", "2012-03-26 06:00:00", "2012-03-26
>       12:00:00",
>       "2012-03-26 18:00:00", "2012-03-27 00:00:00", "2012-03-27
>       06:00:00",
>       "2012-03-27 12:00:00", "2012-03-27 18:00:00", "2012-03-28
>       00:00:00",
>       "2012-03-28 06:00:00", "2012-03-28 12:00:00", "2012-03-28
>       18:00:00",
>       "2012-03-29 00:00:00", "2012-03-29 06:00:00", "2012-03-29
>       12:00:00",
>       "2012-03-29 18:00:00", "2012-03-30 00:00:00", "2012-03-30
>       06:00:00",
>       "2012-03-30 12:00:00", "2012-03-30 18:00:00", "2012-03-31
>       00:00:00",
>       "2012-03-31 06:00:00", "2012-03-31 12:00:00", "2012-03-31
>       18:00:00",
>       "2012-04-01 00:00:00", "2012-04-01 06:00:00", "2012-04-01
>       12:00:00",
>       "2012-04-01 18:00:00", "2012-04-02 00:00:00", "2012-04-02
>       06:00:00",
>       "2012-04-02 12:00:00", "2012-04-02 18:00:00", "2012-04-03
>       00:00:00",
>       "2012-04-03 06:00:00", "2012-04-03 12:00:00", "2012-04-03
>       18:00:00",
>       "2012-04-04 00:00:00", "2012-04-04 06:00:00", "2012-04-04
>       12:00:00",
>       "2012-04-04 18:00:00", "2012-04-05 00:00:00", "2012-04-05
>       06:00:00",
>       "2012-04-05 12:00:00", "2012-04-05 18:00:00", "2012-04-06
>       00:00:00",
>       "2012-04-06 06:00:00", "2012-04-06 12:00:00", "2012-04-06
>       18:00:00",
>       "2012-04-07 00:00:00", "2012-04-07 06:00:00", "2012-04-07
>       12:00:00",
>       "2012-04-07 18:00:00", "2012-04-08 00:00:00", "2012-04-08
>       06:00:00",
>       "2012-04-08 12:00:00", "2012-04-08 18:00:00", "2012-04-09
>       00:00:00",
>       "2012-04-09 06:00:00", "2012-04-09 12:00:00", "2012-04-09
>       18:00:00",
>       "2012-04-10 00:00:00", "2012-04-10 06:00:00", "2012-04-10
>       12:00:00",
>       "2012-04-10 18:00:00", "2012-04-11 00:00:00", "2012-04-11
>       06:00:00",
>       "2012-04-11 12:00:00", "2012-04-11 18:00:00", "2012-04-12
>       00:00:00",
>       "2012-04-12 06:00:00", "2012-04-12 12:00:00", "2012-04-12
>       18:00:00",
>       "2012-04-13 00:00:00", "2012-04-13 06:00:00", "2012-04-13
>       12:00:00",
>       "2012-04-13 18:00:00", "2012-04-14 00:00:00", "2012-04-14
>       06:00:00",
>       "2012-04-14 12:00:00", "2012-04-14 18:00:00", "2012-04-15
>       00:00:00",
>       "2012-04-15 06:00:00", "2012-04-15 12:00:00", "2012-04-15
>       18:00:00",
>       "2012-04-16 00:00:00", "2012-04-16 06:00:00", "2012-04-16
>       12:00:00",
>       "2012-04-16 18:00:00", "2012-04-17 00:00:00", "2012-04-17
>       06:00:00",
>       "2012-04-17 12:00:00", "2012-04-17 18:00:00", "2012-04-18
>       00:00:00",
>       "2012-04-18 06:00:00", "2012-04-18 12:00:00", "2012-04-18
>       18:00:00",
>       "2012-04-19 00:00:00", "2012-04-19 06:00:00", "2012-04-19
>       12:00:00",
>       "2012-04-19 18:00:00", "2012-04-20 00:00:00", "2012-04-20
>       06:00:00",
>       "2012-04-20 12:00:00", "2012-04-20 18:00:00", "2012-04-21
>       00:00:00",
>       "2012-04-21 06:00:00", "2012-04-21 12:00:00", "2012-04-21
>       18:00:00",
>       "2012-04-22 00:00:00", "2012-04-22 06:00:00", "2012-04-22
>       12:00:00",
>       "2012-04-22 18:00:00", "2012-04-23 00:00:00", "2012-04-23
>       06:00:00",
>       "2012-04-23 12:00:00", "2012-04-23 18:00:00", "2012-04-24
>       00:00:00",
>       "2012-04-24 06:00:00", "2012-04-24 12:00:00", "2012-04-24
>       18:00:00",
>       "2012-04-25 00:00:00", "2012-04-25 06:00:00", "2012-04-25
>       12:00:00",
>       "2012-04-25 18:00:00", "2012-04-26 00:00:00", "2012-04-26
>       06:00:00",
>       "2012-04-26 12:00:00", "2012-04-26 18:00:00", "2012-04-27
>       00:00:00",
>       "2012-04-27 06:00:00", "2012-04-27 12:00:00", "2012-04-27
>       18:00:00",
>       "2012-04-28 00:00:00", "2012-04-28 06:00:00", "2012-04-28
>       12:00:00",
>       "2012-04-28 18:00:00", "2012-04-29 00:00:00", "2012-04-29
>       06:00:00",
>       "2012-04-29 12:00:00", "2012-04-29 18:00:00", "2012-04-30
>       00:00:00",
>       "2012-04-30 06:00:00", "2012-04-30 12:00:00", "2012-04-30
>       18:00:00",
>       "2012-05-01 00:00:00", "2012-05-01 06:00:00", "2012-05-01
>       12:00:00",
>       "2012-05-01 18:00:00", "2012-05-02 00:00:00", "2012-05-02
>       06:00:00",
>       "2012-05-02 12:00:00", "2012-05-02 18:00:00", "2012-05-03
>       00:00:00",
>       "2012-05-03 06:00:00", "2012-05-03 12:00:00", "2012-05-03
>       18:00:00",
>       "2012-05-04 00:00:00", "2012-05-04 06:00:00", "2012-05-04
>       12:00:00",
>       "2012-05-04 18:00:00", "2012-05-05 00:00:00", "2012-05-05
>       06:00:00",
>       "2012-05-05 12:00:00", "2012-05-05 18:00:00", "2012-05-06
>       00:00:00",
>       "2012-05-06 06:00:00", "2012-05-06 12:00:00", "2012-05-06
>       18:00:00",
>       "2012-05-07 00:00:00", "2012-05-07 06:00:00", "2012-05-07
>       12:00:00",
>       "2012-05-07 18:00:00", "2012-05-08 00:00:00", "2012-05-08
>       06:00:00",
>       "2012-05-08 12:00:00", "2012-05-08 18:00:00", "2012-05-09
>       00:00:00",
>       "2012-05-09 06:00:00", "2012-05-09 12:00:00", "2012-05-09
>       18:00:00",
>       "2012-05-10 00:00:00", "2012-05-10 06:00:00", "2012-05-10
>       12:00:00",
>       "2012-05-10 18:00:00", "2012-05-11 00:00:00", "2012-05-11
>       06:00:00",
>       "2012-05-11 12:00:00", "2012-05-11 18:00:00", "2012-05-12
>       00:00:00",
>       "2012-05-12 06:00:00", "2012-05-12 12:00:00", "2012-05-12
>       18:00:00",
>       "2012-05-13 00:00:00", "2012-05-13 06:00:00", "2012-05-13
>       12:00:00",
>       "2012-05-13 18:00:00", "2012-05-14 00:00:00", "2012-05-14
>       06:00:00",
>       "2012-05-14 12:00:00", "2012-05-14 18:00:00", "2012-05-15
>       00:00:00",
>       "2012-05-15 06:00:00", "2012-05-15 12:00:00", "2012-05-15
>       18:00:00",
>       "2012-05-16 00:00:00", "2012-05-16 06:00:00", "2012-05-16
>       12:00:00",
>       "2012-05-16 18:00:00", "2012-05-17 00:00:00", "2012-05-17
>       06:00:00",
>       "2012-05-17 12:00:00", "2012-05-17 18:00:00", "2012-05-18
>       00:00:00",
>       "2012-05-18 06:00:00", "2012-05-18 12:00:00", "2012-05-18
>       18:00:00",
>       "2012-05-19 00:00:00", "2012-05-19 06:00:00", "2012-05-19
>       12:00:00",
>       "2012-05-19 18:00:00", "2012-05-20 00:00:00", "2012-05-20
>       06:00:00",
>       "2012-05-20 12:00:00", "2012-05-20 18:00:00", "2012-05-21
>       00:00:00",
>       "2012-05-21 06:00:00", "2012-05-21 12:00:00", "2012-05-21
>       18:00:00",
>       "2012-05-22 00:00:00", "2012-05-22 06:00:00", "2012-05-22
>       12:00:00",
>       "2012-05-22 18:00:00", "2012-05-23 00:00:00", "2012-05-23
>       06:00:00",
>       "2012-05-23 12:00:00", "2012-05-23 18:00:00", "2012-05-24
>       00:00:00",
>       "2012-05-24 06:00:00", "2012-05-24 12:00:00", "2012-05-24
>       18:00:00",
>       "2012-05-25 00:00:00", "2012-05-25 06:00:00", "2012-05-25
>       12:00:00",
>       "2012-05-25 18:00:00", "2012-05-26 00:00:00", "2012-05-26
>       06:00:00",
>       "2012-05-26 12:00:00", "2012-05-26 18:00:00", "2012-05-27
>       00:00:00",
>       "2012-05-27 06:00:00", "2012-05-27 12:00:00", "2012-05-27
>       18:00:00",
>       "2012-05-28 00:00:00", "2012-05-28 06:00:00", "2012-05-28
>       12:00:00",
>       "2012-05-28 18:00:00", "2012-05-29 00:00:00", "2012-05-29
>       06:00:00",
>       "2012-05-29 12:00:00"), class = "factor"), basistime =
>       structure(c(1L,
>       1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
>       1L, 1L,
>       1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
>       2L, 2L,
>       2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L,
>       3L, 3L,
>       3L), .Label = c("2012-01-25 15:02:00", "2012-01-26
>       15:11:00",
>       "2012-01-27 01:41:00", "2012-01-27 10:15:00", "2012-01-27
>       15:15:00",
>       "2012-01-28 14:22:00", "2012-01-29 13:33:00", "2012-01-30
>       14:11:00",
>       "2012-01-31 14:24:00", "2012-02-01 14:55:00", "2012-02-02
>       14:56:00",
>       "2012-02-03 14:40:00", "2012-02-04 15:01:00", "2012-02-05
>       15:04:00",
>       "2012-02-06 14:37:00", "2012-02-07 14:42:00", "2012-02-08
>       14:44:00",
>       "2012-02-09 14:27:00", "2012-02-10 14:33:00", "2012-02-11
>       15:05:00",
>       "2012-02-12 15:09:00", "2012-02-13 15:00:00", "2012-02-14
>       15:10:00",
>       "2012-02-15 14:46:00", "2012-02-16 14:42:00", "2012-02-17
>       14:14:00",
>       "2012-02-18 15:27:00", "2012-02-19 13:13:00", "2012-02-20
>       13:56:00",
>       "2012-02-21 14:39:00", "2012-02-22 15:33:00", "2012-02-23
>       15:14:00",
>       "2012-02-24 15:14:00", "2012-02-25 14:25:00", "2012-02-26
>       14:08:00",
>       "2012-02-27 14:55:00", "2012-02-28 14:40:00", "2012-02-29
>       14:45:00",
>       "2012-03-01 15:18:00", "2012-03-02 15:18:00", "2012-03-03
>       15:43:00",
>       "2012-03-04 15:16:00", "2012-03-05 15:17:00", "2012-03-06
>       15:03:00",
>       "2012-03-07 14:44:00", "2012-03-08 14:53:00", "2012-03-09
>       15:10:00",
>       "2012-03-10 14:43:00", "2012-03-11 13:37:00", "2012-03-12
>       14:58:00",
>       "2012-03-13 14:36:00", "2012-03-14 13:49:00", "2012-03-15
>       14:32:00",
>       "2012-03-16 15:01:00", "2012-03-17 13:55:00", "2012-03-18
>       13:44:00",
>       "2012-03-19 13:55:00", "2012-03-20 13:53:00", "2012-03-21
>       14:07:00",
>       "2012-03-22 14:03:00", "2012-03-23 14:30:00", "2012-03-24
>       14:47:00",
>       "2012-03-25 14:32:00", "2012-03-26 14:41:00", "2012-03-27
>       13:51:00",
>       "2012-03-28 13:32:00", "2012-03-29 13:59:00", "2012-03-30
>       14:15:00",
>       "2012-03-31 14:12:00", "2012-04-01 14:30:00", "2012-04-02
>       13:43:00",
>       "2012-04-03 13:54:00", "2012-04-04 13:45:00", "2012-04-05
>       13:46:00",
>       "2012-04-06 13:41:00", "2012-04-07 13:13:00", "2012-04-08
>       12:59:00",
>       "2012-04-09 13:53:00", "2012-04-10 14:15:00", "2012-04-11
>       14:26:00",
>       "2012-04-12 14:05:00", "2012-04-13 13:37:00", "2012-04-14
>       13:52:00",
>       "2012-04-15 15:00:00", "2012-04-16 14:42:00", "2012-04-17
>       14:21:00",
>       "2012-04-18 14:40:00", "2012-04-19 14:35:00", "2012-04-20
>       15:14:00",
>       "2012-04-21 14:46:00", "2012-04-22 14:44:00", "2012-04-23
>       14:33:00",
>       "2012-04-24 14:41:00", "2012-04-25 14:13:00", "2012-04-26
>       14:19:00",
>       "2012-04-27 14:35:00", "2012-04-28 13:48:00", "2012-04-29
>       14:12:00",
>       "2012-04-30 13:53:00", "2012-05-02 14:41:00", "2012-05-03
>       15:01:00",
>       "2012-05-04 15:21:00", "2012-05-05 14:57:00", "2012-05-06
>       14:09:00",
>       "2012-05-07 14:30:00", "2012-05-08 14:05:00", "2012-05-08
>       21:21:00",
>       "2012-05-09 15:02:00", "2012-05-10 14:27:00", "2012-05-11
>       14:47:00",
>       "2012-05-12 13:24:00", "2012-05-13 14:40:00", "2012-05-13
>       19:24:00",
>       "2012-05-14 14:33:00", "2012-05-15 14:39:00", "2012-05-16
>       14:07:00",
>       "2012-05-17 13:42:00", "2012-05-18 14:30:00", "2012-05-19
>       13:59:00",
>       "2012-05-20 14:14:00", "2012-05-21 14:15:00", "2012-05-22
>       14:18:00",
>       "2012-05-23 14:14:00", "2012-05-24 13:52:00"), class =
>       "factor"),
>          fcst = c(38.7, 38.9, 39.2, 39.8, 40.5, 41.5, 42.5,
>       43.1,
>          43.9, 44.5, 44.8, 45, 45, 45.1, 45.4, 45.8, 46.4, 47,
>       47.5,
>          47.9, 39.2, 40, 41.8, 42.2, 42.8, 44.4, 45.7, 46.2,
>       46.2,
>          46.2, 46.5, 47, 47.5, 47.9, 48.4, 49, 49.5, 49.9, 50.2,
>       50.4,
>          41.3, 42.5, 42.8, 42.8, 42.8, 42.9, 43, 43.3, 43.5,
>       43.8),
>          usgs = c(38.5, 38.6, 38.6, 38.6, 39.1, 39.8, 41.2,
>       42.9,
>          43.4, 43.6, 43.4, 43.1, 43, 43.1, 43.5, 43.8, 44.1,
>       44.2,
>          44.4, 44.5, 39.1, 39.8, 41.2, 42.9, 43.4, 43.6, 43.4,
>       43.1,
>          43, 43.1, 43.5, 43.8, 44.1, 44.2, 44.4, 44.5, 44.5,
>       44.5,
>          44.6, 44.2, 41.2, 42.9, 43.4, 43.6, 43.4, 43.1, 43,
>       43.1,
>          43.5, 43.8)), .Names = c("date", "basistime", "fcst",
>       "usgs"
>       ), row.names = c(NA, 50L), class = "data.frame")
>
>       aggregate(fcst ~ basistime,data=legacy, FUN= max)
>
>       A snippet...
>
>                    basistime fcst
>       1   2012-01-25 15:02:00 47.9
>       2   2012-01-26 15:11:00 50.4
>       3   2012-01-27 01:41:00 46.0
>       4   2012-01-27 10:15:00 47.3
>       5   2012-01-27 15:15:00 47.3
>       6   2012-01-28 14:22:00 46.2
>       7   2012-01-29 13:33:00 45.8
>       8   2012-01-30 14:11:00 44.8
>       9   2012-01-31 14:24:00 43.9
>       10  2012-02-01 14:55:00 41.1
>       11  2012-02-02 14:56:00 38.1
>       12  2012-02-03 14:40:00 36.2
>       13  2012-02-04 15:01:00 34.7
>       14  2012-02-05 15:04:00 33.1
>       15  2012-02-06 14:37:00 32.2
>
>       This is what I want, except I need the other corresponding
>       date-time column
>       as well. I've tried this with the date-times as factors
>       and as POSIXct
>       values and using many of the combinations suggested in the
>       documentation
>       and other examples. The closest I can get returns the
>       second date as a
>       numeric value:
>
>       aggregate(cbind(fcst,date) ~ basistime,data=legacy, FUN=
>       max)
>
>       Produces:
>
>                    basistime fcst       date
>       1   2012-01-25 15:02:00 47.9 1327942800
>       2   2012-01-26 15:11:00 50.4 1328029200
>       3   2012-01-27 01:41:00 46.0 1328072400
>       4   2012-01-27 10:15:00 47.3 1328032800
>       5   2012-01-27 15:15:00 47.3 1328115600
>       6   2012-01-28 14:22:00 46.2 1328202000
>       7   2012-01-29 13:33:00 45.8 1328288400
>       8   2012-01-30 14:11:00 44.8 1328374800
>       9   2012-01-31 14:24:00 43.9 1328461200
>       10  2012-02-01 14:55:00 41.1 1328547600
>       11  2012-02-02 14:56:00 38.1 1328634000
>       12  2012-02-03 14:40:00 36.2 1328720400
>       13  2012-02-04 15:01:00 34.7 1328806800
>       14  2012-02-05 15:04:00 33.1 1328893200
>       15  2012-02-06 14:37:00 32.2 1328979600
>       16  2012-02-07 14:42:00 31.2 1329066000
>       17  2012-02-08 14:44:00 30.4 1329152400
>       18  2012-02-09 14:27:00 30.0 1329238800
> 
>
>       Help is greatly appreciated!
>
>       Regards,
>       Tom
>
>       --
> 
>         [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more,
> see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible
> code.
> 
> 
> ---------------------------------------------------------------------------
> 
> Jeff Newmiller                        The     .....       .....  Go
> Live...
> DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
> Go...
>                                       Live:   OO#.. Dead: OO#.. 
> Playing
> Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
> /Software/Embedded Controllers)               .OO#.       .OO#. 
> rocks...1k
> ---------------------------------------------------------------------------
> 
> 
> 
> 
> --
> Thomas E Adams, III1724 Sage Lane
> Blacksburg, VA 24060
> tea3rd at gmail.com (personal)
> tea at terrapredictions.org (work)
> 
> 1 (513) 739-9512 (cell)
> 
> 
>

---------------------------------------------------------------------------
Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
                                       Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...1k
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