[R] How to assign week numbers to a time-series

[Achim Zeileis]

On Fri, 5 Mar 2010, Hosack, Michael wrote:

> Hello everyone,
>
> My progress has stalled on finding a way of creating a somewhat complicated variable to add to my existing dataframe and I am hoping one of you could help me out. The dataframe below contains only a fraction of the data of my complete dataframe, but all of the variables. What I want to do is add another variable named 'WEEK' to this dataframe that is assigned 1 for row 1 and remains 1 until the first SAT (i.e. Saturday) under variable 'DOW' (day of week) occurs, at which point variable 'WEEK' is now assigned 2. 'WEEK' should continue to be assigned 2 until the following SAT under variable 'DOW' at which variable 'WEEK' will now be assigned 3, and so on. In this scheme, weekdays are such that SAT=1, SUN=2, MON=3,.....FRI=7. I am basically trying to assign week numbers to potential sampling days in a survey season for use in a program that will generate a fisheries creel survey schedule. I should note that if element 1 happens to have DOW=SAT (that is the case this year, sin!
 ce!
>  the first day of our survey 05/01 is a Saturday), then WEEK 1 begins on day 1 (05/01/2010) and WEEK 2 will begin on the first SAT under variable DOW. I hope I explained this clearly enough, if not let me know.

If I understand correctly, then you can easily do the following:
   - create a "Date" object with YR-MM-DD
   - compute the number of days since origin (2010-04-30 in your case)
   - compute integer division by 7 plus 1

In one step:

   as.numeric(as.Date(paste(YR, MM, DD, sep = "-")) -
     as.Date("2010-04-30")) %/% 7 + 1

BTW: Some of the rest of your information (like DOW) could also be easily 
inferred from the "Date", e.g., via transformation to POSIXlt:

   as.POSIXlt(as.Date("2010-05-01"))$wday

hth,
Z

> Mike
>
>         MM DD YR DOW DOW. DTYPE  TOD  TOD. SITENUM       DESC
> 1         05 01 2010 SAT        1     2            MORN    1     101         WALNUT.CK
> 185    05 01 2010 SAT         1     2            MORN    1     102           LAMPE
> 369    05 01 2010 SAT         1     2            MORN    1     103          EAST.AVE
> 553    05 01 2010 SAT         1     2           MORN    1     104          NORTH.EAST
> 737    05 01 2010 SAT         1     2          AFTN       2     101           WALNUT.CK
> 921    05 01 2010 SAT         1     2          AFTN       2     102            LAMPE
> 1105 05 01 2010 SAT          1     2         AFTN       2     103           EAST.AVE
> 1289 05 01 2010 SAT         1     2          AFTN       2     104           NORTH.EAST
> 2        05 02 2010 SUN        2     2          MORN    1     101           WALNUT.CK
> 186   05 02 2010 SUN        2     2          MORN    1     102            LAMPE
> 370   05 02 2010 SUN        2     2          MORN    1     103            EAST.AVE
> 554   05 02 2010 SUN         2     2         MORN    1     104           NORTH.EAST
> 738   05 02 2010 SUN         2     2         AFTN      2     101            WALNUT.CK
> 922   05 02 2010 SUN         2     2          AFTN     2     102              LAMPE
> 1106 05 02 2010 SUN          2     2       AFTN       2     103            EAST.AVE
> 1290 05 02 2010 SUN        2     2          AFTN      2     104            NORTH.EAST
> 3        05 03 2010 MON        3     1        MORN    1     101           WALNUT.CK
> 187   05 03 2010 MON    3     1           MORN    1     102               LAMPE
> 371   05 03 2010 MON      3     1          MORN    1     103           EAST.AVE
> 555   05 03 2010 MON      3     1          MORN    1     104           NORTH.EAST
> 739   05 03 2010 MON    3     1           AFTN      2     101            WALNUT.CK
> 923   05 03 2010 MON      3     1          AFTN      2     102               LAMPE
> 1107 05 03 2010 MON      3     1          AFTN      2     103            EAST.AVE
> 1291 05 03 2010 MON         3     1      AFTN      2     104            NORTH.EAST
> 4        05 04 2010 TUE          4     1         MORN    1     101           WALNUT.CK
> 188   05 04 2010 TUE         4     1           MORN    1     102           LAMPE
> 372   05 04 2010 TUE          4     1        MORN     1     103            EAST.AVE
> .          .    .       .           .           .       .               .            .           .                    .
>
> 	[[alternative HTML version deleted]]
>
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