Convert list/vector of strings with date format into posix date class with R

Question

I have a list of strings that is in our date format and I want to convert it into a list of posix dates that I can manipulate with R, how can I do that?

This is what I have but I end up with a list of lists:

 a <- c("2009.01.01 00:00:00", "2009.01.01 00:00:00")

z <- lapply(a,function(x){strptime(x, "%Y.%m.%d %H:%M:%S")})

> z <- lapply(a,function(x){strptime(x, "%Y.%m.%d %H:%M:%S")})
> summary(z)
     Length Class   Mode
[1,] 1      POSIXlt list
[2,] 1      POSIXlt list

Note that a isn't a list, it's a vector (in R's terms). strptime is vectorized (see joran's answer), which means it works on all instances of that vector. If you indeed had a list, lapply would be appropriate. Also notice that z IS a list of vectors (and not a list of lists). — Roman Luštrik

joran joran · Accepted Answer · 2012-01-26T18:08:29

strptime is vectorized:

a <- c("2009.01.01 12:20:10", "2009.01.01 04:12:14")
> out <- strptime(a, "%Y.%m.%d %H:%M:%S")
> str(out)
 POSIXlt[1:2], format: "2009-01-01 12:20:10" "2009-01-01 04:12:14"

Convert list/vector of strings with date format into posix date class with R

2 Answers