How to run two indices in r-CodePudding

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,

CodePudding user response：

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.

CodePudding user response：

Another way to write your function is using expand.grid over l lists of sequences of length l.

f <- \(l) do.call(paste,
                  cbind(expand.grid(replicate(l - 1, seq.int(l), simplify=FALSE)), 
                        sep=', '))
f(3)
# [1] "1, 1" "2, 1" "3, 1" "1, 2" "2, 2" "3, 2" "1, 3" "2, 3" "3, 3"

f(4)
#  [1] "1, 1, 1" "2, 1, 1" "3, 1, 1" "4, 1, 1" "1, 2, 1" "2, 2, 1" "3, 2, 1"
#  [8] "4, 2, 1" "1, 3, 1" "2, 3, 1" "3, 3, 1" "4, 3, 1" "1, 4, 1" "2, 4, 1"
# [15] "3, 4, 1" "4, 4, 1" "1, 1, 2" "2, 1, 2" "3, 1, 2" "4, 1, 2" "1, 2, 2"
# [22] "2, 2, 2" "3, 2, 2" "4, 2, 2" "1, 3, 2" "2, 3, 2" "3, 3, 2" "4, 3, 2"
# [29] "1, 4, 2" "2, 4, 2" "3, 4, 2" "4, 4, 2" "1, 1, 3" "2, 1, 3" "3, 1, 3"
# [36] "4, 1, 3" "1, 2, 3" "2, 2, 3" "3, 2, 3" "4, 2, 3" "1, 3, 3" "2, 3, 3"
# [43] "3, 3, 3" "4, 3, 3" "1, 4, 3" "2, 4, 3" "3, 4, 3" "4, 4, 3" "1, 1, 4"
# [50] "2, 1, 4" "3, 1, 4" "4, 1, 4" "1, 2, 4" "2, 2, 4" "3, 2, 4" "4, 2, 4"
# [57] "1, 3, 4" "2, 3, 4" "3, 3, 4" "4, 3, 4" "1, 4, 4" "2, 4, 4" "3, 4, 4"
# [64] "4, 4, 4"

Note: "R version 4.1.2 (2021-11-01)".