# [R] How to select max data according to week?

Bert Gunter bgunter@4567 @end|ng |rom gm@||@com
Tue Jun 18 20:38:28 CEST 2019

```My apologies. I negected to cc r-help. -- Bert

On Tue, Jun 18, 2019 at 11:21 AM Bert Gunter <bgunter.4567 using gmail.com> wrote:

>
> I assume that 20000215 means year 2000, month 2, day 15.
> I also assume that you want maxes for the first 2 weeks of a month, the
> second 2 weeks, and any remaining days.
> I also assume that this might be desired for arbitrary numbers of years,
> months, and days.
>
> The following is one way to do this. As it's a slight pain to cut and
> paste email data as text into R (use ?dput or R code to run to provide
> example data instead), I just made up my own. You'll have to do the
> following within a data frame through extraction or by using with() of
> course.
>
> ## create some example data for 3 months in 2000
> d<- 2e7 +c(113:131,201:228, 301:330) ## dates
> conc <- runif(length(d)) # concentrations
>
> ## convert the date to character to extract year, month, and day
> cdate <- as.character(d)
> ## use substr to to the extraction
> year <- substr(cdate,1,4)
> mon <- substr(cdate,5,6)
> day <- substr(cdate, 7,8)
>
> ## convert day to numeric and use cut() to group into the biweekly periods.
> d14 <- cut(as.numeric(day), c(0,14.5,28.5, 32))
>
> ## Use tapply() to create your desired table of results.
> tapply(conc, list(year, d14, mon), max, na.rm = TRUE)
>
> ## Results
>
> , , 01
>
>       (0,14.5] (14.5,28.5] (28.5,32]
> 2000 0.7357389   0.9655391 0.7962965
>
> , , 02
>
>       (0,14.5] (14.5,28.5] (28.5,32]
> 2000 0.8193979   0.9487207        NA
>
> , , 03
>
>       (0,14.5] (14.5,28.5] (28.5,32]
> 2000 0.9718919   0.9997093  0.168659
>
>
> Cheers,
> Bert
>
> Bert Gunter
>
>
>
>
> On Tue, Jun 18, 2019 at 8:53 AM SITI AISYAH BINTI ZAKARIA <
> aisyahzakaria using unimap.edu.my> wrote:
>
>> Hi,
>>
>> I'm Aisyah..I have a problem to run my R coding. I want to select maximum
>> value according to week.
>>
>> here is my data
>>
>> Date          O3_Conc
>> 20000101        0.033
>> 20000102        0.023
>> 20000103        0.025
>> 20000104        0.041
>> 20000105        0.063
>> 20000106        0.028
>> 20000107        0.068
>> 20000108        0.048
>> 20000109        0.037
>> 20000110        0.042
>> 20000111        0.027
>> 20000112        0.035
>> 20000113        0.063
>> 20000114        0.035
>> 20000115        0.042
>> 20000116        0.028
>>
>> I want to find the max value from column O3_Conc for only 14 days that
>> refer to biweekly in month. And the next 14 days for the max value.
>>
>> I hope that I can get the result like this:
>>
>> Date                     Max O3_Conc
>> 20000101 - 20000114        0.068
>> 20000115 - 20000129        0.061
>>
>> I try many coding but still unavailable.
>>
>> this example my coding
>>
>> library(plyr)
>>       data.frame(CA0003)
>>
>>       # format weeks as per requirement (replace "00" with "52" and
>>       tmp <- list()
>>       tmp\$y <- format(df\$Date, format="%Y")
>>       tmp\$w <- format(df\$Date, format="%U")
>>       tmp\$y[tmp\$w=="00"] <- as.character(as.numeric(tmp\$y[tmp\$w=="00"]) -
>> 14)
>>       tmp\$w[tmp\$w=="00"] <- "884"
>>       df\$week <- paste(tmp\$y, tmp\$w, sep = "-")
>>
>>       # get summary
>>       df2 <- ddply(df, .(week),transform, O3_Conc=max(O3_Conc))
>>
>>       # include week ending date
>>       tmp\$week.ending <- lapply(df2\$week, function(x) rev(df[df\$week ==x,
>> "O3_Conc"])[[1]])
>>       df2\$week.ending <- sapply(tmp\$week.ending, max(O3_Conc, TRUE)
>>
>> output
>>         Site_Id Site_Location                                       Date
>>       Year    O3_Conc Month   Day     week
>> 1       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000101
>>       2000    0.033   1       1       NULL-NULL
>> 2       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000102
>>       2000    0.023   1       2       NULL-NULL
>> 3       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000103
>>       2000    0.025   1       3       NULL-NULL
>> 4       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000104
>>       2000    0.041   1       4       NULL-NULL
>> 5       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000105
>>       2000    0.063   1       5       NULL-NULL
>> 6       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000106
>>       2000    0.028   1       6       NULL-NULL
>> 7       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000107
>>       2000    0.068   1       7       NULL-NULL
>> 8       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000108
>>       2000    0.048   1       8       NULL-NULL
>> 9       CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000109
>>       2000    0.037   1       9       NULL-NULL
>> 10      CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000110
>>       2000    0.042   1       10      NULL-NULL
>> 11      CA0003  Sek. Keb. Cederawasih, Taman Inderawasih, Perai 20000111
>>       2000    0.027   1       11      NULL-NULL
>>
>>
>>
>>
>> --
>> This message has been scanned by E.F.A. Project and is believed to be
>> clean.
>>
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