[R] NAs and row/column calculations

[Jim Bouldin]

I continue to have great frustrations with NA values--in particular making
summary calculations on rows or cols of a matrix containing them.  For
example, why does:

> a = matrix(1:30,nrow=5)
> is.na(a[c(1:2),c(3:4)]);a
     [,1] [,2] [,3] [,4] [,5] [,6]
[1,]    1    6   NA   NA   21   26
[2,]    2    7   NA   NA   22   27
[3,]    3    8   13   18   23   28
[4,]    4    9   14   19   24   29
[5,]    5   10   15   20   25   30
> apply(a[!is.na(a)],2,sum)

give me this:

"Error in apply(a[!is.na(a)], 2, sum) : dim(X) must have a positive length"

when

> dim(a)
[1] 5 6

What is the trick to calculating summary values from rows or columns
containing NAs?  Drives me nuts.  More nuts that is.

Thanks.




Jim Bouldin, PhD
Research Ecologist
Department of Plant Sciences, UC Davis
Davis CA, 95616
530-554-1740