Calculates the sum for each row (column) in a matrix.
rowSums2(x, rows = NULL, cols = NULL, na.rm = FALSE, dim. = dim(x),
  ..., useNames = TRUE)colSums2(x, rows = NULL, cols = NULL, na.rm = FALSE, dim. = dim(x),
  ..., useNames = TRUE)
Returns a numeric
vector of
length N (K).
A vector indicating subset of rows to
operate over. If NULL, no subsetting is done.
A vector indicating subset of columns to
operate over. If NULL, no subsetting is done.
If TRUE, missing values are
excluded.
An integer vector of
length two specifying the dimension of x, also when not a
matrix.  Comment: The reason for this argument
being named with a period at the end is purely technical (we get a run-time
error if we try to name it dim).
Not used.
If FALSE (default), no naming
support is done. Else if TRUE, names attributes
of result are set.
Henrik Bengtsson
The implementation of rowSums2() and colSums2() is
optimized for both speed and memory.