Replace missing values with a value from another column

Question

If I have:

s <- data.frame(ID=c(191, 282, 202, 210), Group=c(\"\", \"A\", \"\", \"B\"), stringsAsFactors=FALSE)
s
   ID Group
1 191      
2 282     A
3 20         


        

Answer 1

We can use data.table to assign the values in "Group2" to "Group" where the "Group" is "" specified in the "i" condition.

library(data.table)
setDT(s)[Group=="", Group:= Group2]

As the assignment happens in place, it is considered to be efficient.