[R] Column-by-column division

Eric Berger er|cjberger @end|ng |rom gm@||@com
Wed Mar 3 21:18:35 CET 2021


Why not use standard matrix multiplication which is straightforward here:

x %*% diag(1/s)

HTH,
Eric


On Wed, Mar 3, 2021 at 7:13 AM Harold Doran <
harold.doran using cambiumassessment.com> wrote:

> To make sure the scalar is used instead of using the recycled vector s,
> maybe like this
>
> x <- matrix(1:20, nrow=10)
> s <- c(1,2)
> sapply(1:2, function(i) x[,i]/s[i])
>
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Steven Yen
> Sent: Wednesday, March 3, 2021 6:00 AM
> To: R-help Mailing List <r-help using r-project.org>
> Subject: [R] Column-by-column division
>
> I have a 10 x 2 matrix x. Like to divide the first column by s[1] and
> second column by s[2]. The following lines work but are clumsy. Any idea?
> Thanks.
>
>  > x
>        [,1] [,2]
>   [1,]    1   11
>   [2,]    2   12
>   [3,]    3   13
>   [4,]    4   14
>   [5,]    5   15
>   [6,]    6   16
>   [7,]    7   17
>   [8,]    8   18
>   [9,]    9   19
> [10,]   10   20
>  > s
> [1] 1 2
>  > t(t(x)/s)
>        [,1] [,2]
>   [1,]    1  5.5
>   [2,]    2  6.0
>   [3,]    3  6.5
>   [4,]    4  7.0
>   [5,]    5  7.5
>   [6,]    6  8.0
>   [7,]    7  8.5
>   [8,]    8  9.0
>   [9,]    9  9.5
> [10,]   10 10.0
>
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> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>

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