[R] Warning: matrix by vector division

[Benilton Carvalho]

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
>
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