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

test <- read.table(textConnection("     col1   col2    col3
1    23    17      NA
2    55    NA      NA
3    24    12      13
4    34    23      12"))

> table(test$col2,useNA="ifany")

  12   17   23  
   1    1    1    1 
> table(test$col3,useNA="ifany")

  12   13  
   1    1    2