Message-ID: <42F392A8.2040900@stats.uwo.ca>
Date: 2005-08-05T16:24:08Z
From: Duncan Murdoch
Subject: Computing sums of the columns of an array
In-Reply-To: <42F390E9.3010301@metahuman.org>
On 8/5/2005 12:16 PM, Martin C. Martin wrote:
> Hi,
>
> I have a 5x731 array A, and I want to compute the sums of the columns.
> Currently I do:
>
> apply(A, 2, sum)
>
> But it turns out, this is slow: 70% of my CPU time is spent here, even
> though there are many complicated steps in my computation.
>
> Is there a faster way?
You'd probably do better with matrix multiplication:
rep(1, nrow(A)) %*% A
Duncan Murdoch