How to run two indices in r

I am struggeling with a VERY simple problem :

I would like to run 2 indices combinations in a loop : i=1,j=1, i=1,j=2,i=1,j=3…..
then switch to i=1,j=2 i=2,j=2 i=3,j=2… and so on until i=n,j=n

I wrote the following code which sadly doesn’t work properly :

• I cannot use r functions such as expand.grid etc..

a <- function(n) {
  for (i in 1:n)  {
    for (j in 1:n) {
     print(i,j)
    }
  }
}

#I expect to get 1,1 1,2 1,3 1,4… 2,1 2,2… but this is not the result.

Thank you in advance,

>Solution :

Your code does work! Just printing with comma only prints the first.

Instead try separating by comma in a string:

a <- function(n) {
  for (i in 1:n)  {
    for (j in 1:n) {
     print(paste(i, j, sep=', '))
    }
  }
}

Ex:

> a(3)
[1] "1, 1"
[1] "1, 2"
[1] "1, 3"
[1] "2, 1"
[1] "2, 2"
[1] "2, 3"
[1] "3, 1"
[1] "3, 2"
[1] "3, 3"
> 

Your code only prints the numbers on the left.