How to fill NAs with LOCF by factors in data frame, split by country

Question

I have the following data frame (simplified) with the country variable as a factor and the value variable has missing values:

country value
AUT     NA
AUT            


        

Answer 1

A modern version of the ddply solution is to use the package dplyr:

library(dplyr)
DF %>%
  group_by(county) %>% 
  mutate(value = na.locf(value, na.rm = F))