使用as.POSIXct用R转换日期

Question

I'm working with dates and R and I'm converting dates using the as.POSIXct function. I have a pretty good understanding of how to convert dates by just looking at the ?strptime docs. However I'm confused about why this specific conversion doesn't work as expected (see below).

date_string <- "03/11/2017, 3:14:32 pm"
as.POSIXct(date_string, format = "%m/%d/%Y, %H:%M:%S",tz="PST8PDT")

> [1] "2017-03-11 03:14:32 PST" 

I'm losing 12 hours of time with this conversion, I'm expecting this..

> [1] "2017-03-11 15:14:32 PST"

I've tried using '%r' with my formatting but that always gives me NA's? Can somebody explain what R is doing here, and why it's not converting this date string as expected?

Answer 1

Two mistakes:

• you used %H where you want %I for the dreaded 12-hour format
• you omitted %p to catch the "pm" marker

With that corrected:

R> date_string <- "03/11/2017, 3:14:32 pm"
R> as.POSIXct(date_string, format = "%m/%d/%Y, %I:%M:%S %p",tz="PST8PDT")
[1] "2017-03-11 15:14:32 PST"
R>