Use apply over rows

Question

I have a simple dataframe.

  V1 V2 V3
1  1  4  7
2  2  5  8
3  3  6  9

I would like to divide the entries in each row by the sum of all entries in that row, and get this:

  V1 V2 V3
1  0.08 0.33 0.58
2  0.13 0.33 0.53
3  0.16 0.33 0.50

It's pretty simple to use mydf[1,]/sum(mydf[1,]) and repeat it 3 times, but this is tedious.

I have an intuitive feeling that an apply function would work.

I have a vague notion I need to:
1) Put mydf[1,]/sum(mydf[1,]) in a functional wrapper
2) use apply(myfunction, 1, mydataframe)

But I'm not sure what the arguments to myfunction would be.

I'm a little confused on this and any help is appreciated.

Answer 1

dat <- data.frame(matrix(1:9, nrow=3))
dat / rowSums(dat)

You could also use apply, but it will return a matrix (and require you to transpose with t).

t(apply(dat, 1, FUN=function(x) x / sum(x)))