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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Entropy/Erlang/entropy.erl Normal file
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-module( entropy ).
-export( [shannon/1, task/0] ).
shannon( String ) -> shannon_information_content( lists:foldl(fun count/2, dict:new(), String), erlang:length(String) ).
task() -> shannon( "1223334444" ).
count( Character, Dict ) -> dict:update_counter( Character, 1, Dict ).
shannon_information_content( Dict, String_length ) ->
{_String_length, Acc} = dict:fold( fun shannon_information_content/3, {String_length, 0.0}, Dict ),
Acc / math:log( 2 ).
shannon_information_content( _Character, How_many, {String_length, Acc} ) ->
Frequency = How_many / String_length,
{String_length, Acc - (Frequency * math:log(Frequency))}.