Summing lots of Vectors; row-wise or elementwise, but ignoring NA values

Question

I am trying to create a new vector that is the sum of 35 other vectors. The problem is that there are lots of NA values, but for this particular use, I want to treat those as zeros. Adding the vectors won't work, because if any of the 35 vectors contain an NA, the result is NA. Here is the example of the problem:

col1<-c(NA,1,2,3)
col2<-c(1,2,3,NA)
col3<-c(NA,NA,2,3)
Sum<-col1+col2+col3
Sum
# [1] NA NA  7 NA

I want the result to be 1, 3, 7, 6.
I suppose I could create new versions of each of the vectors in which I replace the NA with a 0, but that would be a lot of work when applied to 35 vectors. Is there a simple function that will help me out?

Answer 1

Could also have used the rowSums function:

rowSums( cbind (col1,col2,col3), na.rm=TRUE)
#[1] 1 3 7 6

?rowSums   # also has colSums described on same help page

Answer 2

Put them in a matrix first:

apply(cbind(col1,col2,col3),1,sum,na.rm = TRUE)
[1] 1 3 7 6

You can read about each function here using R's built-in documentation: ?apply, ?cbind.

cbind stands for "column bind": it takes several vectors or arrays and binds them "by column" into a single array:

cbind(col1,col2,col3)
     col1 col2 col3
[1,]   NA    1   NA
[2,]    1    2   NA
[3,]    2    3    2
[4,]    3   NA    3

apply, well, applies a function (sum in this case) to either the rows or columns of a matrix. This allows us to use the na.rm = TRUE argument to sum so that the NA values are dropped.