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Duplicates of expand.grid for 2 Variables

Source: R/utils.R
grid_dup.Rd

Create a vector of element positions of duplicates in the output of expand.grid on 2 identical vectors. An efficient method of creating combinations for 2 variables.

Usage

grid_dup(n, omit.id)

Arguments

n

the length of vector passed to expand.grid().

omit.id

(optional) set to TRUE to also select the elements where the 2 items are identical. The output of expand.grid, subset to remove duplicates with 'omit.id' set to TRUE would be the equivalent of utils::combn(n, 2).

Value

A numeric vector.

Examples

n <- 3
expand.grid(1:n, 1:n)
#>   Var1 Var2
#> 1    1    1
#> 2    2    1
#> 3    3    1
#> 4    1    2
#> 5    2    2
#> 6    3    2
#> 7    1    3
#> 8    2    3
#> 9    3    3
expand.grid(1:n, 1:n)[-grid_dup(n), ]
#>   Var1 Var2
#> 1    1    1
#> 2    2    1
#> 3    3    1
#> 5    2    2
#> 6    3    2
#> 9    3    3
expand.grid(1:n, 1:n)[-grid_dup(n, omit.id = TRUE), ]
#>   Var1 Var2
#> 2    2    1
#> 3    3    1
#> 6    3    2