Question

I am looking to make a simple code in R to generate a matrix like the one below..

I know you start one like:

 for(i in 1:10){

But I am not sure where to go from here. I know I can just use outer(1:10,1:10) but am looking to use a for() do() statement.

    1   2   3   4   5   6   7   8   9   10
 1  1   2   3   4   5   6   7   8   9   10  
 2  2   4   6   8   10  12  14  16  18  20  
 3  3   6   9   12  15  18  21  24  27  30  
 4  4   8   12  16  20  24  28  32  36  40  
 5  5   10  15  20  25  30  35  40  45  50  
 6  6   12  18  24  30  36  42  48  54  60  
 7  7   14  21  28  35  42  49  56  63  70  
 8  8   16  24  32  40  48  56  64  72  80  
 9  9   18  27  36  45  54  63  72  81  90 
 10 10  20  30  40  50  60  70  80  90 100  

Answer 1

for me to explain outer, you need 2 loops ( at least how I would do if I want to implement it)

v <- c()
for(i in 1:10)
  for(j in 1:10)
    v <- c(v,i*j)      ## This is SLOW! (naughty)
matrix(v,ncol=10,nrow=10)

EDIT

In my last implementation I allocate dynamically the size of the matrix which is very slow. It is better to allocate the matrix before the loops, something like this:

xx <- matrix(NA,ncol=10,nrow=10)
for(i in 1:10)
  for(j in 1:10)
    xx[i,j] <- i*j 

Another way to do with vectors:

I <- 1:10
J <- 1:10
I %*% t(J)