A matrix with number of columns equal to length(columns).
Arguments
object
object that may be coerced to a matrix
columns
list in which each component is a vector of subscripts for columns to be pooled
...
other arguments (not used currently)
Details
The first element of columns defines the columns of object
for the first new column, the second for the second new column etc.
This is a generic method. More useful methods exist for capthist and
traps objects.