Thanks for your suggestion. I received a few error messages. Can anyone help me figure out why I get the following error messages and how to solve them by revising my code? The data is shown in the post above. Thanks.
> library(zoo) > > colClasses <- c("character", "character", "numeric", "character", > "character", "numeric") > > col.names <- c("date", "day", "time", "webpage", "item", "value") > > # z <- read.zoo("myfile.dat", skip = 1, index = as.list(1:5), > z <- read.zoo(testdata[,1:5],as.Date(as.character(testdata[, 1])),skip = > 1, index = as.list(1:6), + format = "%d/%m/%Y", col.names = col.names, + aggregate = function(x) tail(x, 1), colClasses = colClasses) Error in `[.data.frame`(rval, , j) : undefined columns selected > > > # extract all Thursdays and Fridays > z45 <- z[format(time(z), "%w") %in% 4:5,] Error: object 'z' not found > > # keep last entry in each week > # and show result on R console > z45[!duplicated(format(time(z45), "%U"), fromLast = TRUE), ] Error: object 'z45' not found -- View this message in context: http://r.789695.n4.nabble.com/How-to-extract-Friday-data-from-daily-data-tp3029050p3034553.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list 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.