Convert 12 hour to 24 hour format in R

Question

I am not getting the right conversion when I try to convert 12 hours to 24 hours. My script (with sample data is below).

library(lubridate)
library(data.table)

# Read Sample Data
df <- data.frame(c("April 22 2016 10:49:15 AM","April 22 2016 10:01:21 AM","April 22 2016 09:06:40 AM","April 21 2016 09:50:49 PM","April 21 2016 06:07:18 PM"))
colnames(df) <- c("Date") # Set Column name
dt <- setDT(df) # Convert to data.table

ff <- function(x) as.POSIXlt(strptime(x,"%B %d %Y %H:%M:%S %p"))
dt[,dates := as.Date(ff(Date))]

When I try creating a new variable called TOD, I get the output in H:M:S format without converting it into 24 hour format. What I mean is that for the 3rd row, instead of getting 21:50:49 I get 09:50:49. I tried two different ways to do this. One use as.ITime from data.table and then also using strptime. The code I use to calculate TOD is below.

dt[,TOD1 := as.ITime(ff(Date))]
dt$TOD2 <- format(strptime(dt$Date, "%B %d %Y %H:%M:%S %p"), format="%I:%M:%S")

I thought of trying it using dataframe instead of data.table to eliminate any issues with using strptime in data.table and still got the same answer.

df$TOD <- format(strptime(df$Date, "%B %d %Y %H:%M:%S %p"), format="%I:%M:%S") # Using dataframe instead of data.table

Any insights on how to get the right answer?

Answer 1

Here you go:

library(lubridate)
df$Date <- mdy_hms(df$Date)

Note that while mdy_hms is extremely convenient and takes care of the 12 / 24 hour time for you, it will automatically assign UTC as a time zone. You can specify a different one if you need. You can then convert df to a data.table if you like.

Answer 2

As commented @lmo, you need to use %I parameter instead of %H , from ?strptime :

%H
Hours as decimal number (00–23). As a special exception strings such as 24:00:00 are accepted for input, since ISO 8601 allows these.

%I
Hours as decimal number (01–12).

strptime("April 21 2016 09:50:49 PM", "%B %d %Y %I:%M:%S %p")
# [1] "2016-04-21 21:50:49 EDT"