combos: Ordered Combinations

In quantreg: Quantile Regression

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)

quantreg documentation built on Aug. 19, 2023, 5:09 p.m.