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

[SITI AISYAH BINTI ZAKARIA]

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 adjust corresponding year)
      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.