On 23 Sep 2014, at 23:30 , Rolf Turner <r.tur...@auckland.ac.nz> wrote:
> On 24/09/14 03:10, carol white wrote:
>> Hi, If I want to divide the column of a matrix by the sum of the
>> column, should I loop over the columns or can I use apply family?
>
> m1 <- apply(m,2,function(x){x/sum(x)})
>
> should do what you want IIUYC.
It might, but there's a surprise if you do the same thing with rows.
The canonical construction is
sweep(M, 2, apply(M, 2, sum), "/")
although efficiency suggests replacing the apply() with colSums(M) nowadays.
>
> cheers,
>
> Rolf Turner
>
> --
> Rolf Turner
> Technical Editor ANZJS
>
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