Nested While-Loop - R - r

Question

So I have a table m, consisting of a random number of rows and columns. (can be any size)...
I want to do this calculation against each rows/columns totals:
r[i] * c[j] / n;
Where r <- rowSums(m);, c <- colSums(m); and n <- sum(m);
I can do it with a double for-loop but I'm hoping to implement it now using while loops.
I wasn't going to use while loops but seems the table size can differ, I figured it was wise too.
I'm storing each value as it's found in a test vector.
This is my attempt, but I'm messing up the indices:
while(i < nrow(m)){
while(j < ncol(m)){
test[i] <- r[i]*c[j] / n;
j=j+1;
i=i+1;
}
j=j+1;
i=i+1;
}
Any guidance to help me sort out my loops would be much appreciated. Thanks in advance.
update
See below for an example and expected result:
m <- t(matrix(c(28,48,10,114), nrow=2, ncol=2));
r <- rowSums(m); #76 124 (sum of rows)
c <- colSums(m); #38 162 (sum of cols)
n <- sum(m); #200 (sum of all cells)
test <- c(0, times length(m)); #empty vector/data frame
#inside while loops, calc for each r and c indice:
test[1] <- 76 *38 /200 #first calc to test[i] where i=1
test[2] <- 124*38 /200
test[3] <- 76*162 /200
test[4] <- 124*162/200 #last calc to test[i] where i==length(m)

Answer 1

I would avoid using a for or while loop and do something like this instead:
> as.vector(outer(r,c, function(x,y) x*y/n))
[1] 14.44 23.56 61.56 100.44

Answer 2

No need to use a while loop. It is always best to use vector operations in R (and any other array-based language). It makes for clearer and faster code.
nrows<-sample(1:100,1) # a random number of rows
ncols<-sample(1:100,1) # a random number of columns
#create a matrix of random numbers with our random dimnesions
m<-matrix(runif(nrows*ncols), nrow=nrows)
n<-sum(m)
#read into outer, it creates a cartesian product of your vectors
#so you will have every r[i] multipled with every r[j]...ie what your loop is doing
r<-outer(rowSums(m),colSums(m),function(x,y) x*y/n)
Hope this helps, let me know if you have any questions.

Answer 3

A more R-like solution would be to use expand.grid instead of a nested while loop:
Set-up:
> m <- matrix(1:12, 3, 4)
> m
[,1] [,2] [,3] [,4]
[1,] 1 4 7 10
[2,] 2 5 8 11
[3,] 3 6 9 12
> n <- sum(m)
> r <- rowSums(m)
> c <- colSums(m)
Now:
> test <- expand.grid(r,c)
> test
Var1 Var2
1 22 6
2 26 6
3 30 6
4 22 15
5 26 15
6 30 15
7 22 24
8 26 24
9 30 24
10 22 33
11 26 33
12 30 33
> test <- test[,1] * test[,2] / n
> test
[1] 1.692308 2.000000 2.307692 4.230769 5.000000 5.769231 6.769231
[8] 8.000000 9.230769 9.307692 11.000000 12.692308