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

The tidyverse way, albeit not using locf, is:

library(tidyverse)

data %>% 
    group_by(country) %>% 
    fill(value)

Source: local data frame [9 x 2]
Groups: country [2]

country value
(fctr) (dbl)
1     AUT    NA
2     AUT     5
3     AUT     5
4     AUT     5
5     GER    NA
6     GER    NA
7     GER     7
8     GER     7
9     GER     7

Answer 2

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))