Re: [R] Warning: matrix by vector division

From: Benilton Carvalho <bcarvalh_at_jhsph.edu>
Date: Fri, 07 Mar 2008 17:43:49 -0500

and you might want to check ?prop.table

 > prop.table(a, 2)

      [,1] [,2]

[1,]  0.0 0.3333333
[2,]  0.5 0.3333333
[3,]  0.5 0.3333333

or even ?sweep (which will be useful for more complex situations)

 > sweep(a, 2, colSums(a), "/")

      [,1] [,2]

[1,]  0.0 0.3333333
[2,]  0.5 0.3333333
[3,]  0.5 0.3333333

b

On Mar 7, 2008, at 5:32 PM, Alexey Shipunov wrote:

> Dear list,
>
> I just made a very simple mistake, but it was hard to spot. And I
> think that I should warn other people, because it is probably so
> simple to make...
>
> === R code ===
>
> # Let us create a matrix:
> (a <- cbind(c(0,1,1), rep(1,3)))
>
> # [,1] [,2]
> # [1,] 0 1
> # [2,] 1 1
> # [3,] 1 1
>
> # That is a MISTAKE:
> a/colSums(a)
>
> # [,1] [,2]
> # [1,] 0.0000000 0.3333333
> # [2,] 0.3333333 0.5000000
> # [3,] 0.5000000 0.3333333
> # I just wonder if some R warning should be issued here?
>
> # That is what I actually needed (column-wise frequencies):
> t(t(a)/colSums(a))
>
> # [,1] [,2]
> # [1,] 0.0 0.3333333
> # [2,] 0.5 0.3333333
> # [3,] 0.5 0.3333333
>
> === end of R code ===
>
> With best wishes and regards,
> Alexey Shipunov
>
> ______________________________________________
> R-help_at_r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 07 Mar 2008 - 22:47:50 GMT

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