Change a date column in multiple data frames with one function

Asked Oct 14 '16 at 09:11

Active Oct 14 '16 at 09:11

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I know there are several questions regarding the "apply one function to multiple data frames"-issue. However, I coundn't find a solution to my problem but I think I got close to it using a solution from this question: Same function over multiple data frames in R

I have 12 data frames with 4 columns each. The second one contains the data as an integer (e.g. 20161014, so %Y%m%d). To get it into 2016-10-14 I used

 TX_SOUID100758.txt[,2]<-as.Date(as.character(TX_SOUID100758.txt[,2]), "%Y%m%d")

Since I want to apply this function on all 15 data frames I tried

zch_filelist <- list.files(path=path, pattern="*.txt")
for (file in zch_filelist){
  assign(file, read.csv(paste(path, file, sep=''),na.strings = -9999))
}
lapply(zch_filelist, function(x) (as.Date(as.character(x[2]), "%Y%m%d")))

I used the previously created list of file names when I imported the files into R. However, it is not working. I guess the mistake is the indexing in the as.date function. Any help is greatly appreciated. Thanks!

edited May 23 '17 at 12:13

Community

asked Oct 14 '16 at 09:11

David Hoffmann

You need to use ?mapply. – Chirayu Chamoli Oct 14 '16 at 09:18
thanks, but how do I addess the second vector in each data frame? – David Hoffmann Oct 14 '16 at 10:18
your zch_filelist should be a list in order to use lapply. – Chirayu Chamoli Oct 14 '16 at 10:28
ok, now my data frames are in a list. but how do I address the second column in each data frame? 'lapply(zch_data[[]][,2], function(x) (as.Date(as.character(x), "%Y%m%d")))' does not work.. – David Hoffmann Oct 14 '16 at 12:07
2

you can use this: `lapply(listofdf, function(x) (as.Date(as.character(x[,2]), "%Y%m%d")))`. – Chirayu Chamoli Oct 14 '16 at 12:17
Since this has been answered, ought to be closed as no longer reproducible. – IRTFM Nov 22 '16 at 21:17

Change a date column in multiple data frames with one function

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