[R] sparse matrix from vector outer product
flying-sheep at web.de
Wed Jan 14 15:02:40 CET 2015
creating a matrix from two vectors a, b by multiplying each combination can
be done e.g. via
a %*% t(b)
outer(a, b) # default for third argument is '*'
But this yields a normal matrix.
Is there an efficient way to create sparse matrices (from the Matrix
package) like that?
Right now i’m doing
a.sparse = as(a, 'sparseVector')
b.sparse = as(t(b), 'sparseMatrix')
a.sparse %*% b.sparse
but this strikes me as wasteful.
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