How do you extract the time unit when using difftime()?

Question

I'm currently running a for loop code and at the end of each loop I am measuring the duration of the loop and print a message that tells the user how long did the loop take.

To get the duration I'm using

duration <- difftime(end_time, start_time) 

And this is how I print the statement

print(paste("Loop", i, "took", duration, "to run.")). 

The problem is the duration of each loop may range from 30 seconds to 1 hour. Putting the duration inside the paste just turns it into a number without the unit in it.

e.g.

print(paste("Loop", i, "took", duration, "to run.")). 
"Loop 5 took 10.5 to run"

How do I get the unit from the difftime() in order to get something like: "Loop 5 took 10.5 minutes to run."

PS: Some may suggest standardizing the duration by declaring the "unit" argument in difftime() but I want the duration to be easily understood by the user that's why I set the unit to default "auto".

Answer 1

Call units from duration to get the unit and get the numeric value by subsetting duration:

print(paste("Loop", i, "took", round(duration[[1]], 2),  units(duration), "to run."))

Here is an example:

start_time <- Sys.time()

# few seconds later
end_time <- Sys.time()

duration <- difftime(end_time, start_time)

print(paste("Loop", 1, "took", round(duration[[1]], 2),  units(duration), "to run."))

Result:

[1] "Loop 1 took 6.97 secs to run."

The unit would be automatic depending on the range of the duration. See this ohter example:

start_time <- Sys.time()

# few days later
end_time <- as.Date("2019-01-23")

duration <- difftime(end_time, start_time)

print(paste("Loop", 1, "took", round(duration[[1]], 2),  units(duration), "to run."))

Result:

> print(paste("Loop", 1, "took", round(duration[[1]], 2),  units(duration), "to run."))
[1] "Loop 1 took 5.9 days to run."

Answer 2

One way is to capture the output from difftime as it is using capture.output

start_time <- as.POSIXct('2019-01-01 02:34:00')
end_time <- as.POSIXct('2019-01-01 03:14:00')

paste("Loop 5 took", capture.output(difftime(end_time, start_time)), "to run.")
#[1] "Loop 5 took Time difference of 40 mins to run."

Now you can change the output to make it meaningful, say remove "Time difference of " from the output

sent <- capture.output(difftime(end_time, start_time))
paste("Loop 5 took",sub("Time difference of ","", sent) , "to run.")
#[1] "Loop 5 took 40 mins to run."

For another input

start_time <- as.POSIXct('2019-01-01 02:34:00')
end_time <- as.POSIXct('2019-01-01 02:34:50')

sent <- capture.output(difftime(end_time, start_time))
paste("Loop 5 took",sub("Time difference of ","", sent) , "to run.")
#[1] "Loop 5 took 50 secs to run."