Combinations iterator

This function returns a Combinations iterator for iterating combinations of k items from n items. The iterator allows users to fetch the next combination(s) via the getnext() method.

icombinations(
  x = NULL,
  k = NULL,
  n = NULL,
  v = NULL,
  freq = NULL,
  replace = FALSE,
  skip = 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

skip

the number of combinations skipped

Details

The Combinations class can be initialized by using the convenient wrapper icombinations or

Combinations$new(n, k, v = NULL, freq = NULL, replace = FALSE)

getnext(d = 1L, layout = NULL, drop = NULL)
collect(layout = "row")
reset()

d

number of fetched arrangements

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

drop

vectorize a matrix or unlist a list

See also

combinations for generating all combinations and ncombinations to calculate number of combinations

Super classes

arrangements::abstractiter -> arrangements::iter -> arrangements::Arrangements -> Combinations

Methods

Public methods

• Combinations$new()

• Combinations$reset()

• Combinations$collect()

• Combinations$getnext()

• Combinations$print()

• Combinations$clone()

Inherited methods

• arrangements::Arrangements$nextElem()

---

Method new()

Usage

Combinations$new(n, k, v = NULL, freq = NULL, replace = FALSE, skip = NULL)

---

Method reset()

Usage

Combinations$reset()

---

Method collect()

Usage

Combinations$collect(layout = "row")

---

Method getnext()

Usage

Combinations$getnext(d = 1L, layout = NULL, drop = NULL)

---

Method print()

Usage

Combinations$print(...)

---

Method clone()

The objects of this class are cloneable with this method.

Usage

Combinations$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Examples

icomb <- icombinations(5, 2)
icomb$getnext()
#> [1] 1 2
icomb$getnext(2)
#>      [,1] [,2]
#> [1,]    1    3
#> [2,]    1    4
icomb$getnext(layout = "column", drop = FALSE)
#>      [,1]
#> [1,]    1
#> [2,]    5
# collect remaining combinations
icomb$collect()
#>      [,1] [,2]
#> [1,]    2    3
#> [2,]    2    4
#> [3,]    2    5
#> [4,]    3    4
#> [5,]    3    5
#> [6,]    4    5

library(foreach)
#> Error in library(foreach): there is no package called ‘foreach’
foreach(x = icombinations(5, 2), .combine=c) %do% {
  sum(x)
}
#> Error in foreach(x = icombinations(5, 2), .combine = c) %do% {    sum(x)}: could not find function "%do%"