iterors (version 1.0)

icombinations: Iterator that generates all combinations of a vector taken m at a time.

Description

Constructs an iterator generates all combinations of a vector taken m at a time. This function is similar to combn.

Usage

icombinations(object, m, replacement = FALSE)

Value

iterator that generates all combinations of object

Arguments

object

vector

m

the length of each combination

replacement

Generate combinations with replacement? Default: no.

Details

By default, the combinations are without replacement so that elements are not repeated. To generate combinations with replacement, set replacement=TRUE.

The function implementation is loosely based on the combinations function from Python's itertools. Combinations with replacement are based on combinations_with_replacement from the same Python library.

Examples

# Combinations without replacement
it <- icombinations(1:4, m=2)

nextOr(it, NA) # c(1, 2)
nextOr(it, NA) # c(1, 3)
nextOr(it, NA) # c(1, 4)
nextOr(it, NA) # c(2, 3)
nextOr(it, NA) # c(2, 4)
nextOr(it, NA) # c(3, 4)

# Combinations without replacement
it <- icombinations(1:4, m=2, replacement=TRUE)

nextOr(it, NA) # c(1, 1)
nextOr(it, NA) # c(1, 2)
nextOr(it, NA) # c(1, 3)
nextOr(it, NA) # c(1, 4)
nextOr(it, NA) # c(2, 2)
nextOr(it, NA) # c(2, 3)
nextOr(it, NA) # c(2, 4)
nextOr(it, NA) # c(3, 3)
nextOr(it, NA) # c(3, 4)
nextOr(it, NA) # c(4, 4)

it3 <- icombinations(1:5, m=2)
as.list(it3)
utils::combn(x=1:5, m=2, simplify=FALSE)