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

Here's a ddply solution. Try this

library(plyr)
ddply(DF, .(country), na.locf)
  country value
1     AUT  
2     AUT     5
3     AUT     5
4     AUT     5
5     GER  
6     GER  
7     GER     7
8     GER     7
9     GER     7

Edit From ddply help you can find that

.variables:  variables to split data frame by, 
as quoted variables, a formula or character vector.

so another alternatives to get what you want are:

ddply(DF, "country", na.locf)
ddply(DF, ~country, na.locf)

note that replacing .variables with DF$variable is not allowed, that's why you got an error when doing this.

DF is your data.frame