Question

This is a really simple question, but I am hoping someone will be able to help me avoid extra lines of unnecessary code. I have a simple dataframe:

Df.1 <- data.frame(A = c(5,4,7,6,8,4),B = (c(1,5,2,4,9,1)),C=(c(2,3,NA,5,NA,9)))

What I want to do is produce an extra column which is the multiplication of A, B and C, which I will then cbind to the original dataframe.

So, I would normally use:

attach(Df.1)
D<-A*B*C

But obviously where the NAs are in column C, I get an NA in variable D. I don’t want to exclude all the NA rows, rather just ignore the NA values in this column (and then the value in D would simply be the multiplication of A and B, or where C was available, A*B*C.

I know I could simply replace the NAs with 1s, so the calculation remains unchanged, or use if statements, but I was wodnering what the simplist way of doing this is?

Any ideas?

Answer 1

You can use prod which has an na.rm argument. To do it by row use apply:

apply(Df.1,1,prod,na.rm=TRUE)
[1]  10  60  14 120  72  36