Combine/merge columns while avoiding NA?

Question

I have a really simple problem but haven\'t been able to find a solution. I am hoping someone can help. I have a dataframe test3:

test3 <- st         


        

Answer 1

Here's one approach:

> transform(test3, C=rowSums(test3, na.rm=TRUE))
   A  B C
1  1 NA 1
2  2 NA 2
3 NA  3 3
4  4 NA 4

Consider the following data.frame test3 with an additional column AA, you can use the operator [ to subet the columns you are interested in:

> set.seed(1) # adding a new column
> test3$AA <- rnorm(4, 10, 1)
> test3  # this is how test3 looks like
   A  B        AA
1  1 NA  9.373546
2  2 NA 10.183643
3 NA  3  9.164371
4  4 NA 11.595281
> transform(test3, C=rowSums(test3[, c("A", "B")], na.rm=TRUE))
   A  B        AA C
1  1 NA  9.373546 1
2  2 NA 10.183643 2
3 NA  3  9.164371 3
4  4 NA 11.595281 4