Calculating Time Difference between two columns

11
votes

After converting factors in POSIXCT format and then applying datetime format, I want to take the difference of datetime between 2 pos1 and pos2.

However, when I do that for a specific item I get the right answer in the console but when I do the operation on the whole set the console outputs just number and also the dateframe reflects those number as you can see.

How can I get the hours in the dataframe when I am trying to take the difference? I am using lubridate package, is there any function to do so?

Here is some example code/picture of the data in RStudio describing it

CR_Date <- data.frame(
  pos1="2014-07-01 00:00:00",
  pos2=c("2014-07-01 00:00:00","2014-07-01 10:15:00")
)
CR_Date[] <- lapply(CR_Date,as.POSIXct)
CR_Date

#        pos1                pos2
#1 2014-07-01 2014-07-01 00:00:00
#2 2014-07-01 2014-07-01 10:15:00

CR_Date$pos2[2] - CR_Date$pos1[2]
#Time difference of 10.25 hours
CR_Date$hours <- CR_Date$pos2 - CR_Date$pos1

enter image description here

2
rdatetimelubridate
It is in second, not in hour. You can divide CR_date by 3600. – user3710546

2 Answers

24
votes

Firstly, this has nothing to do with lubridate.

Secondly, RStudio has let you down by screwing with the printing of the variable in the display window. If you enter CR_Date$hours in the command line window you will see it prints

#Time differences in secs
#[1]     0 36900

and head(CR_Date) gives:

#        pos1                pos2      hours
#1 2014-07-01 2014-07-01 00:00:00     0 secs
#2 2014-07-01 2014-07-01 10:15:00 36900 secs

Either of which would have tipped you off as to what it is displaying.

As @Victorp suggests, difftime is the way to resolve this:

CR_Date$hours <- with(CR_Date, difftime(pos2,pos1,units="hours") )
CR_Date

#        pos1                pos2       hours
#1 2014-07-01 2014-07-01 00:00:00  0.00 hours
#2 2014-07-01 2014-07-01 10:15:00 10.25 hours
10
votes

You may also use the "as.double method" and its units argument (see ?diffime):

as.double method [as.double(x, units = "auto", ...)] returns the numeric value expressed in the specified units

...where x is

an object inheriting from class "difftime"

Applied to your example, where pos2 - pos1 will result in a difftime object:

CR_Date$hours <- as.double(CR_Date$pos2 - CR_Date$pos1, units = "hours")
CR_Date

#        pos1                pos2 hours
#1 2014-07-01 2014-07-01 00:00:00  0.00
#2 2014-07-01 2014-07-01 10:15:00 10.25

Or other units: 

as.double(CR_Date$pos2 - CR_Date$pos1, units = "mins")
#[1]   0 615

as.double(CR_Date$pos2 - CR_Date$pos1, units = "days")
#[1] 0.0000000 0.4270833