20 lines
646 B
Erlang
20 lines
646 B
Erlang
-module( entropy ).
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-export( [shannon/1, task/0] ).
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shannon( String ) -> shannon_information_content( lists:foldl(fun count/2, dict:new(), String), erlang:length(String) ).
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task() -> shannon( "1223334444" ).
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count( Character, Dict ) -> dict:update_counter( Character, 1, Dict ).
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shannon_information_content( Dict, String_length ) ->
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{_String_length, Acc} = dict:fold( fun shannon_information_content/3, {String_length, 0.0}, Dict ),
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Acc / math:log( 2 ).
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shannon_information_content( _Character, How_many, {String_length, Acc} ) ->
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Frequency = How_many / String_length,
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{String_length, Acc - (Frequency * math:log(Frequency))}.
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