Determine the number of rows with NAs

Question

I have a data frame as follows:

     col1   col2    col3
 1    23    17      NA
 2    55    NA      NA
 3    24    12      13
 4    34    23      12

Answer 1

Another solution adding columns 2 and 3:

> sum(is.na(all[,"col2"] + all[,"col3"]))
[1] 2