How can I get diff() to work here? [ I cannt use lag() or lead()]

Question

I am trying to calculate the increase in life expectancy for each country, but I cannot get the diff() function to work here. I also tried the lag/lead functions but I cannot use that. Any advise is appreciated.

library(gapminder)
gm <- gapminder
inclife <- gm %>%
   drop_na(lifeExp)%>%
   group_by(country) %>%
   select(country, year, lifeExp) %>%
   mutate(inc = diff(lifeExp))

This is the error I got

Error in `mutate()`:
! Problem while computing `inc = diff(lifeExp)`.
✖ `inc` must be size 12 or 1, not 11.
ℹ The error occurred in group 1: country = "Afghanistan".
Run `rlang::last_error()` to see where the error occurred.

Why can you not use lead/lag? That seems like an odd restriction if you are using dplyr. — MrFlick, Dec 07 '22 at 16:02

score 5 · Accepted Answer · answered Dec 07 '22 at 15:57

Append a NA or another value, since diff will provide a vector of length n-1, and mutate requires that the number of observations does not change.

inclife <- gm %>%
   drop_na(lifeExp)%>%
   group_by(country) %>%
   select(country, year, lifeExp) %>%
   mutate(inc = c(NA,diff(lifeExp)))

How can I get diff() to work here? [ I cannt use lag() or lead()]

1 Answers1