[R] colSums and rowSums with arrays - different classes and dim ?

[Ernesto Jardim]

Hi,

I'm using colSums and rowSums to sum the first dimensions of arrays. It 
works ok but the resulting object is different. See

 > a3d <- array(rnorm(120, mean=2), dim=c(20,6,1))
 > dim(colSums(a3d))
[1] 6 1
 > dim(rowSums(a3d))
NULL
 > class(colSums(a3d))
[1] "matrix"
 > class(rowSums(a3d))
[1] "numeric"

I was expecting rowSums to preserve the array class and the relevant 
dimensions (1,20).

The main problem is with arrays where the third dimension (or higher) is 
 > 1. colSums preserve the array but rowSums concatenate the results:

 > a3d <- array(rnorm(120, mean=2), dim=c(20,3,2))
 > rowSums(a3d)
  [1]  8.894178 11.932361 15.231601 12.374629 11.823671 10.564709  9.065166
  [8] 13.900264 13.331756  9.351242 11.989821  7.643745  9.923288  8.169997
[15] 12.124624 16.711742 11.414150 15.221880 12.053734 13.368988
 > colSums(a3d)
          [,1]     [,2]
[1,] 44.80941 29.49216
[2,] 42.18339 39.81121
[3,] 39.90528 38.89010

Is this on purpose ?

Regards

EJ