combinations: Combinations generator

In arrangements: Fast Generators and Iterators for Permutations, Combinations, Integer Partitions and Compositions

Description

This function generates all the combinations of selecting k items from n items. The results are in lexicographical order.

Usage

combinations(x = NULL, k = NULL, n = NULL, v = NULL, freq = NULL,
  replace = FALSE, layout = NULL, nitem = -1L, skip = NULL,
  index = NULL, nsample = NULL, drop = NULL)

Arguments

x	an integer or a vector, will be treated as n if integer; otherwise, will be treated as v. Should not be specified together with n and v.
k	an integer, the number of items drawn, defaults to n if freq is NULL else sum(freq)
n	an integer, the total number of items, its value may be implicitly deduced from length(v) or length(freq)
v	a vector to be drawn, defaults to 1:n.
freq	an integer vector of item repeat frequencies
replace	an logical to draw items with replacement
layout	if "row", "column" or "list" is specified, the returned value would be a "row-major" matrix, a "column-major" matrix or a list respectively
nitem	number of combinations required, usually used with skip
skip	the number of combinations skipped
index	a vector of indices of the desired combinations
nsample	sampling random combinations
drop	vectorize a matrix or unlist a list

See Also

icombinations for iterating combinations and ncombinations to calculate number of combinations

Examples

# choose 2 from 4
combinations(4, 2)
combinations(LETTERS[1:3], k = 2)

# multiset with frequencies c(2, 3)
combinations(k = 3, freq = c(2, 3))

# with replacement
combinations(4, 2, replace = TRUE)

# column major
combinations(4, 2, layout = "column")

# list output
combinations(4, 2, layout = "list")

# specifc range of combinations
combinations(4, 2, nitem = 2, skip = 3)

# specific combinations
combinations(4, 2, index = c(3, 5))

# random combinations
combinations(4, 2, nsample = 3)

# zero sized combinations
dim(combinations(5, 0))
dim(combinations(5, 6))
dim(combinations(0, 0))
dim(combinations(0, 1))

arrangements documentation built on Sept. 13, 2020, 5:20 p.m.