Convert hour:minute:second (HH:MM:SS) string to proper time class

Question

In the following data frame the 'time' column is character in the format hour:minute:second

id <- c(1, 2, 3, 4) time <- c("00:00:01", "01:02:00", "09:30:01", "14:15:25") df <- data.frame(id, time) 

How can I convert 'time' column to a dedicated time class, so that I can perform arithmetic calculations on it?

Answer 1

Use the function chron in package chron:

time<-c("00:00:01", "01:02:00", "09:30:01", "14:15:25")  library(chron) x <- chron(times=time)  x [1] 00:00:01 01:02:00 09:30:01 14:15:25 

Do some useful things, like calculating the difference between successive elements:

diff(x) [1] 01:01:59 08:28:01 04:45:24 

---

chron objects store the values internally as a fraction of seconds per day. Thus 1 second is equivalent to 1/(60*60*24), or 1/86400, i.e. 1.157407e-05.

So, to add times, one simple option is this:

x + 1/86400 [1] 00:00:02 01:02:01 09:30:02 14:15:26 

Answer 2

Using base R you could convert it to an object of class POSIXct, but this does add a date to the time:

id<-c(1,2,3,4) time<-c("00:00:01","01:02:00","09:30:01","14:15:25") df<-data.frame(id,time,stringsAsFactors=FALSE)  as.POSIXct(df$time,format="%H:%M:%S") [1] "2012-08-20 00:00:01 CEST" "2012-08-20 01:02:00 CEST" [3] "2012-08-20 09:30:01 CEST" "2012-08-20 14:15:25 CEST" 

But that does allow you to perform arithmetic calculations on them.