Dear R-helpers,
I have a three-column matrix with lots of rows:
xyzs - matrix(rnorm(3*10,0,1),ncol=3)
# And I am multiplying it with some vector V, and summing the rows
(columns after t()) in this way:
V - c(2,3,4)
system.time(vx - apply(t(xyzs) * V, 2 ,sum))
Ok, this does not take long
Message-
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf Of Remko Duursma
Sent: Tuesday, 1 June 2010 4:04 PM
To: r-help@r-project.org
Subject: [R] Faster matrix operation?
Dear R-helpers,
I have a three-column matrix with lots of rows:
xyzs - matrix(rnorm(3
...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf Of Remko Duursma
Sent: Tuesday, 1 June 2010 4:04 PM
To: r-help@r-project.org
Subject: [R] Faster matrix operation?
Dear R-helpers,
I have a three-column matrix with lots of rows:
xyzs- matrix(rnorm(3*10,0,1),ncol=3)
# And I am
On 1 June 2010 11:34, Peter Ehlers ehl...@ucalgary.ca wrote:
Or, for a very slight further reduction in time in
the case of larger matrices/vectors:
as.vector(tcrossprod(V, xyzs))
I mention this merely to remind new users of the
excellent speed of [t]crossprod().
-Peter Ehlers
Thanks,
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