R: Ordered Combinations

combos {quantreg} | R Documentation

## Ordered Combinations

### Description

All m combinations of the first n integers taken p at a time are computed and return as an p by m matrix. The columns of the matrix are ordered so that adjacent columns differ by only one element. This is just a reordered version of `combn` in base R, but the ordering is useful for some applications.

### Usage

    combos(n,p)

### Arguments

`n` | The n in n choose p
`p` | The p in n choose p

### Value

a `matrix` of dimension p by `choose(n,p)`

### Note

Implementation based on a Pascal algorithm of Limin Xiang and Kazuo Ushijima (2001) translated to ratfor for R. If you have rgl installed you might try `demo("combos")` for a visual impression of how this works.

### References

Limin Xiang and Kazuo Ushijima (2001) "On O(1) Time Algorithms for Combinatorial Generation," Computer Journal, 44(4), 292-302.

### Examples

    H <- combos(20,3)

[Package quantreg version 5.83 Index]