Calculating the difference between consecutive rows by group using dplyr?

Question

I have a dataframe of ids and timestamps. I\'d like to calculate the difference between each sequential timestamp for an individual id.

My dataframe looks like this:

Answer 1

using data.table

library(data.table)
library(dplyr)
setDT(dat)[, time.difference := time - lag(time, 1L), by = id]

Answer 2

Like this:

dat %>% 
  group_by(id) %>% 
  mutate(time.difference = time - lag(time))