lib_combin

Basic combinatorics for Erlang lists and maps.

This library provides basic combinatoric operations like permutation or combinations without replacement for the most common data structures in Erlang: lists and maps.

The documentation of the lib_combin module's API is available online.

Usage

Adding lib_combin to a Project

rebar3

To integrate lib_combin into a rebar3 managed project change the deps entry in your application's rebar.config file to include the tuple {lib_combin, "0.1.5"}.

{deps, [{lib_combin, "0.1.5"}]}.

mix

{:lib_combin, "~> 0.1.5"}

Examples

Combinations without replacement

To enumerate all combinations (order does not matter) without replacement of length 2 by drawing from the list [a, b, c] we use the cnr/2 function as follows:

lib_combin:cnr( 2, [a, b, c] ).
[[b,a],[c,a],[c,b]]

To enumerate all combinations (order does not matter) without replacement of any possible length by drawing from the list [a, b, c] we use the cnr_all/1 function as follows:

lib_combin:cnr_all( [a, b, c] ).
[[],[a],[b],[c],[b,a],[c,a],[c,b],[c,b,a]]

Variations and Permutations

To enumerate all variations (order matters) without replacement of length 2 by drawing from the list [a, b, c] we use the vnr/2 function as follows:

lib_combin:vnr( 2, [a, b, c] ).
[[b,a],[c,a],[a,b],[c,b],[a,c],[b,c]]

To enumerate all permutations (order matters) without replacement from the list [a, b, c] we use the pnr/1 function as follows:

lib_combin:pnr( [a, b, c] ).
[[c,b,a],[b,c,a],[c,a,b],[a,c,b],[b,a,c],[a,b,c]]

Maps

Say, we're leading a burger restaurant which serves burgers made up from a fixed palette of ingredients for bread, meat, and sauce. We can represent the ingredients as an Erlang map in the following way:

Ingredients = #{ sauce => [ketchup, mayo],
                 bread => [sesame, plain],
                 meat  => [beef, chicken, mutton] }.

To find out which burgers can appear on the menu, we use the function permut_map/1 as follows:

lib_combin:permut_map( Ingredients ).
[#{bread => plain,meat => beef,sauce => ketchup},
 #{bread => sesame,meat => beef,sauce => ketchup},
 #{bread => plain,meat => chicken,sauce => ketchup},
 #{bread => sesame,meat => chicken,sauce => ketchup},
 #{bread => plain,meat => mutton,sauce => ketchup},
 #{bread => sesame,meat => mutton,sauce => ketchup},
 #{bread => plain,meat => beef,sauce => mayo},
 #{bread => sesame,meat => beef,sauce => mayo},
 #{bread => plain,meat => chicken,sauce => mayo},
 #{bread => sesame,meat => chicken,sauce => mayo},
 #{bread => plain,meat => mutton,sauce => mayo},
 #{bread => sesame,meat => mutton,sauce => mayo}]

Factorial

The library also contains an implementation of the factorial function.

lib_combin:fac( 4 ).
24

System Requirements

• Erlang OTP 18.0 or higher
• Rebar3 3.0.0 or higher

Resources

• joergen7/gen_pnet A generic Petri net OTP behavior using lib_combin to enumerate transition firing modes.
• seantanly/elixir-combination. An alternative library for combinations and permutations in Elixir.

Authors

• Jorgen Brandt (joergen7) joergen.brandt@onlinehome.de

License

Apache 2.0