# combnPrim: Generate All Combinations of n Elements Taken m at a Time In gRbase: A Package for Graphical Modelling in R

## Description

Generate all combinations of the elements of x taken m at a time. If x is a positive integer, returns all combinations of the elements of seq(x) taken m at a time.

## Usage

 `1` ```combnPrim(x, m, simplify = TRUE) ```

## Arguments

 `x` vector source for combinations, or integer n for x <- seq(n). `m` number of elements to choose. `simplify` logical indicating if the result should be simplified to a matrix; if FALSE, the function returns a list.

## Value

A matrix or a list.

## Note

The combnPrim function is a simplified version of the combn function. However, combnPrim is implemented in C and is considerably faster than combn.

## Author(s)

P. T. Wallace and S<c3><b8>ren H<c3><b8>jsgaard

`combn`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17``` ```x <- letters[1:20] m <- 3 combn(x,m) combnPrim(x,m) combn(m,m) combnPrim(m,m) combn(x,m, simplify=FALSE) combnPrim(x,m, simplify=FALSE) system.time({ for (i in 1:100) { combnPrim(x,m) }}) system.time({ for (i in 1:100) { combn(x,m) }}) system.time({ for (i in 1:100) { combnPrim(x,m, simplify=FALSE) }}) system.time({ for (i in 1:100) { combn(x,m, simplify=FALSE) }}) ```