[R] how to divide each column in a matrix by its colSums?

[Spencer Graves]

prop.table divides every element by the matrix total, not its colSums:

 > m <- matrix(1:4, 2)
 > m
      [,1] [,2]
[1,]    1    3
[2,]    2    4
 > prop.table(m)
      [,1] [,2]
[1,]  0.1  0.3
[2,]  0.2  0.4


       m/rowSums(m) divides every row by its rowSum:

 > m/rowSums(m)
           [,1]      [,2]
[1,] 0.2500000 0.7500000
[2,] 0.3333333 0.6666667


       To divide every element by its colSum:


 > t(t(m)/rowSums(t(m)))
           [,1]      [,2]
[1,] 0.3333333 0.4285714
[2,] 0.6666667 0.5714286


       Hope this helps.
       Spencer


On 11/28/2010 12:55 PM, casperyc wrote:
> In that case, there are values>1,
> which is clearly not what I wanted.
>
> Thanks.
>
> I think I should use prop.table