You need lapply here: df[2:3] <- lapply(df[2:3], as.Date, '%m/%d/%Y')
On Tue, Jun 8, 2010 at 6:19 PM, Horace Tso <horace....@pgn.com> wrote: > Folks, i thought it should be straightforward but after a few hours poking > around, I decided it's best to post my question on this list. > > I have a data frame consisting of a (large) number of date columns, which > are read in from a csv file as character string. I want to convert them to > Date type. Following is an example, where the first column is of integer > type, while the rest are type character. > > > head(df) > TRANSNO TRANS.START_DATE TRANS.END_DATE DIVISION FASB > 1 250897 7/1/2010 7/31/2010 PSTRUCT Z > 2 250617 8/1/2010 8/31/2010 PSTRUCT Z > 3 250364 4/1/2011 6/30/2011 PLR Z > 4 250176 4/1/2011 6/30/2011 PLR Z > 5 250176 4/1/2011 6/30/2011 PLR Z > 6 250364 4/1/2011 6/30/2011 PLR Z > > sapply(df, class) > TRANSNO TRANS.START_DATE TRANS.END_DATE DIVISION > FASB > "integer" "character" "character" "character" > "character" > I thought it's just a matter of applying with a as.Date, > > df[,c(2,3)] = apply(df[,c(2,3)], 2, function(x)as.Date(x,"%m/%d/%Y")) > > Well, the Date conversion fails and I got, > > TRANSNO TRANS.START_DATE TRANS.END_DATE DIVISION FASB > 1 250897 14791 14821 PSTRUCT Z > 2 250617 14822 14852 PSTRUCT Z > 3 250364 15065 15155 PLR Z > 4 250176 15065 15155 PLR Z > 5 250176 15065 15155 PLR Z > 6 250364 15065 15155 PLR Z > The character columns are indeed converted, but they became integer, not > Date type. OK, that's strange and so I started reading the help pages. > > It turns out in apply, the result is coerced to some basic vector types. > And apparently Date is not one of the basic vector types. > > "In all cases the result is coerced by as.vector< > http://127.0.0.1:19182/library/base/help/as.vector> to one of the basic > vector types before the dimensions are set, so that (for example) factor > results will be coerced to a character array. " > > The question then is how type conversion can be carried out on some columns > of a data frame without using a loop. > > Thanks. > > Horace Tso > > > > > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. > -- Henrique Dallazuanna Curitiba-Paraná-Brasil 25° 25' 40" S 49° 16' 22" O [[alternative HTML version deleted]]
______________________________________________ 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.
