Hi Jose,
Jose> I'd like to simply add column-wise using Matrix objects (Csparse).
Jose> It looks like one can apply mosty any base function to these objects
Jose> (i.e., apply, colSums), but there is a nasty conversion to
traditional
Jose> matrix objects if one does that.
not in this case, see below.
Jose> Is there any workaround? I can see colSum listed in the help for
Class
colSums (final 's'!)
Jose> 'CsparseMatrix' , but I wonder whether I'm using the default
colSums() or
Jose> the one specific to CsparseMatrix...
#example
(z = Matrix(c(0,1,0,0), 10,10))
zr = rowSums(z)
class(zr) # numeric; I'd like it to be a CSparseMatrix object
selectMethod("colSums", class(z))
## or
showMethods("colSums")
both show you that you are using the class specific one.
However, why do you assume that colSums() should not return a
numeric vector? From the idea that colSums() and rowSums()
should be fast versions of apply(., marg, sum),
it must return a numeric vector, as it also does for
traditional matrices.
Are your objects so huge that even a 1-row {or 1-column} sparse
matrix would save a lot?
Regards,
Martin Maechler, ETH Zurich
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