[R] Multiplying elements of a list by rows of a matrix

[Bert Gunter]

Clemontina:

As you have seen, the answer is yes, but my question is why bother?
What's wrong with a for() loop?
lapply() should offer no advantage in speed over a loop. Vectorization
could, but lapply() is not vectorization.

-- Bert

On Sun, Nov 11, 2012 at 8:33 AM, Clemontina Davenport <ckalexa2 at ncsu.edu> wrote:
> Hi all,
> I have the following code:
>
> set.seed(1)
> x1 <- matrix(sample(1:12), ncol=3)
> x2 <- matrix(sample(1:12), ncol=3)
> x3 <- matrix(sample(1:12), ncol=3)
> X <- list(x1,x2,x3)
> tt <- matrix(round(runif(5*4),2), ncol=4)
>
> Is there a way I can construct a new list where
> newlist[[i]] = tt[i,] %*% X[[i]]
> without using a for loop? Each element of newlist will be 3 x 1 vector.
>
> Thanks
> --
> Tina Alexander
>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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