dateTime with different format in data frame

Question

I have imported some data into R, which looks like the following:

              dateTime  temp
1 10/25/2005 12:00:00  15.50
2  10/25/2005 1:00:00  15.49
3  10/25/2005 2:00:00  15.52
4  10/25/2005 3:00:00  15.50
5  10/25/2005 4:00:00  15.50
6  10/25/2005 5:00:00  15.46

where the class of the dateTime column of the data.frame is factor and the second column is numeric.

I try to convert the dateTime into POSIXct format as follows:

dat[,1] <- as.POSIXct(dat[,1])

but receive the error

Error in as.POSIXlt.character(as.character(x), ...) : 
  character string is not in a standard unambiguous format

which I think is to do with the dateTime varying in the format that hour is presented e.g. 12, 1, 2 etc and not 12, 01, 02.

How can I change this to POSIXct?

Roland Roland · Accepted Answer · 2013-12-19T08:27:32

You need to specify the format:

datetime <- factor("10/25/2005 12:00:00")

as.POSIXct(datetime)
#Error in as.POSIXlt.character(as.character(x), ...) : 
#  character string is not in a standard unambiguous format

as.POSIXct(datetime, format="%m/%d/%Y %H:%M:%S")
#[1] "2005-10-25 12:00:00 CEST"

Note: I advise you to always specify a time zone explicitly when creating datetime variables. Otherwise, you could get into trouble with daylight saving time.

as.POSIXct(datetime, format="%m/%d/%Y %H:%M:%S", tz="GMT")
#[1] "2005-10-25 12:00:00 GMT"

dateTime with different format in data frame

1 Answers