Dividing each cell in a data set by the column sum in R

Question

I am trying to divide each cell in a data frame by the sum of the column. For example, I have a data frame df:

sample   a   b   c
a2      1    4    6
a3             


        

Answer 1

Given this:

> d = data.frame(sample=c("a2","a3"),a=c(1,5),b=c(4,5),c=c(6,4))
> d
  sample a b c
1     a2 1 4 6
2     a3 5 5 4

You can replace every column other than the first by applying over the rest:

> d[,-1] = apply(d[,-1],2,function(x){x/sum(x)})

> d
  sample         a         b   c
1     a2 0.1666667 0.4444444 0.6
2     a3 0.8333333 0.5555556 0.4

If you don't want d being stomped on make a copy beforehand.