Basic combinatorics for Erlang lists.
APACHE-2.0 License
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.
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"}]}.
{:lib_combin, "~> 0.1.5"}
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]]
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]]
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}]
The library also contains an implementation of the factorial function.
lib_combin:fac( 4 ).
24
lib_combin
to enumerate transition firing modes.