How to make time difference in same units when subtracting POSIXct

Question

I want to subtract to POSIXct. I can do this but depending on the first row (i guess?) the difference will be in seconds or minutes. Below you can see the first diff is in

Answer 1

You can use difftime for that propose which allows you to specify the measurement units, for example

difftime(t1, t2, units = "secs")

Another way (as mentioned by @nicola and is present in the same documentation) is to take advantage of the fact that - has a -.POSIXt method and override the measurement units after the subtraction operation using units<- replacement method

res <- t1 - t2
units(res) <- "secs"