结合r中的两个变量

Question

I think this is a super easy question, but I can't seem to figure it out.

I have two variables: varA and varB .

varA has values 'a' and NA , and varB has values 'b' and NA .

I want to combine them into one variable varC with value 'a' where varA is =='a' and 'b' where varB is =='b' .

I have tried this:

varC <- varA
varC[varB=='b'] <- varB

but I get the error:

Error in [<-.factor(tmp, varB == "b", : NAs are not allowed in subscripted assignments

What am I doing wrong here?

Answer 1

The condition varB=='b' will return NA when varB is NA . Use is.na() to test for NA . Here is an example:

a <- c(NA, 'a', NA)
b <- c('b', NA, 'b')

c <- a
c[is.na(c)] <- b[is.na(c)]

c

[1] "b" "a" "b"