In kota7/combiter: Combinatorics Iterators

knitr::opts_chunk$set(echo = TRUE)

Overview

This package provides iterators for combinations, permutations, subsets, and cartesian product, with which one can go through the elements without creating a huge set of all possible values.

Since v1.0.2, the iterator objects of the package inherit the iter class from iterators package. As a result, the objects are also compatible with foreach library.

Installation and Import

Install from CRAN:

install.packages("combiter")

Install development version:

devtools::install_github("kota7/combiter")

Import:

library(combiter)

Basic Iterators

This package provides four iterator classes for integer vectors: icomb, iperm, isubset, and icartes.

• icomb(n, k) goes through all combinations of k integers out of 1 to n.
• iperm(n, k) goes through all permutations of size k consisting of integers 1 to n of size k.
• isubset(n) goes through all subsets of integers 1 to n.
• icartes(c(n1, n2, ...)), available for v1.0.2+, goes through cartesian products of 1 to n1, 1 to n2 ....

The iterators do not store all possible values inside the object. Instead, they compute the next or previous element on spot. This implementation would be more memory efficient with a large n, since the number of possible cases grows exponentially or even faster for these Combinatorics operations.

Examples

x <- icomb(5, 3)
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}

x <- iperm(4, 2)
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}

x <- isubset(3)
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}

x <- icartes(c(3, 4))
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}

Iterate through Values (v1.0.2+)

Each iterator shown above has its value counterpart. For example, ipermv, the value version of iperm, iterates through all permutations of k elements from n values.

x <- ipermv(c("A", "G", "C"), 2)
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}

icombv, isubsetv, and icartesv are also defined analogously.

Use with foreach (v1.0.2+)

Since v1.0.2, the iterator objects can be used with foreach function from foreach.

library(foreach)
foreach(i = icomb(3, 2)) %do% sum(i)

Links

• combiter (GitHub repository)

kota7/combiter documentation built on June 14, 2025, 11:08 a.m.