Merge two data frame and replace the NA value in R

Question

I have a main table(a), containing column: id, age, and sex. eg.

a <- data.frame(id=letters[1:4], age=c(18,NA,9,NA), sex=c(\"M\",\"F\",\"F\",\"M\"))
  id          


        

Answer 1

We can use data.table

library(data.table)
setDT(a)[b, agei := i.age, on='id'][is.na(age), age := agei][,agei:= NULL][]
a
 #  id age sex
#1:  a  18   M
#2:  b  32   F
#3:  c   9   F
#4:  d  20   M