Parse timestamp with a.m./p.m

问题

I have a file that formats time stamps like 25/03/2011 9:15:00 p.m.

How can I parse this text to a Date-Time class with either strptime or as.POSIXct?

Here is what almost works:

> as.POSIXct("25/03/2011 9:15:00", format="%d/%m/%Y %I:%M:%S", tz="UTC")
[1] "2011-03-25 09:15:00 UTC"

Here is what is not working, but I'd like to have working:

> as.POSIXct("25/03/2011 9:15:00 p.m.", format="%d/%m/%Y %I:%M:%S %p", tz="UTC")
[1] NA

I'm using R version 2.13.2 (2011-09-30) on MS Windows. My working locale is "C":

Sys.setlocale("LC_TIME", "C")

回答1:

It appears the AM/PM indicator can't include punctuation. Try it after removing the punctuation:

td <- "25/03/2011 9:15:00 p.m."
tdClean <- gsub("(.)\\.?[Mm]\\.?","\\1m",td)
as.POSIXct(tdClean, format="%d/%m/%Y %I:%M:%S %p", tz="UTC")
# [1] "2011-03-25 21:15:00 UTC"

回答2:

Just came across this, as another option you can use stringr package.

library(stringr)
data$date2 <- str_sub(data$date, end = -4) 
# this removes the punctuation but holds onto the A/P values
data$date2 <- str_c(data$date2, 'm') 
# adds the required m

来源：https://stackoverflow.com/questions/7883806/parse-timestamp-with-a-m-p-m