Run-length encoding: Difference between revisions

Line 3,494:

=={{header|Mathematica}}/{{header|Wolfram Language}}==

The function

Custom functions using Map, Apply, pure functions, replacing using pattern matching, delayed rules and other functions:

<lang Mathematica>RunLengthEncode[input_String]:=~~StringJoin@@Sequence@@@~~(~~{ToString~~ @~~Length[#]~~,~~First[#]~~}&/@Split[Characters[input]])

RunLengthDecode[input_String]:=StringJoin@@ConstantArray@@@Reverse/@Partition[(Characters[input]/.(ToString[#]->#&/@Range[0,9]))//.{x___,i_Integer,j_Integer,y___}:>{x,10i+j,y},2]</lang>

Example:

⚫

<lang Mathematica>mystring="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";

⚫

RunLengthEncode[mystring]

RunLengthDecode[%]

%==mystring</lang>

gives back:

<lang Mathematica>12W1B12W3B24W1B14W

WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW

⚫

True</lang>

An alternate solution:

<lang Mathematica>RunLengthEncode[s_String] := StringJoin[

{ToString[Length[#]] <> First[#]} & /@ Split[StringSplit[s, ""]]

]

⚫

<lang Mathematica>RunLengthEncode[input_String]:= (l |-> {First@l, Length@l}) /@ (Split@Characters@input)</lang>

RunLengthDecode[s_String] := StringJoin[

Table[#[[2]], {ToExpression[#[[1]]]}] & /@

takes as input an arbitrary string of characters and returns a list of {c, n} pairs, where c is the character and n is the number of repeats. The function

Partition[StringSplit[s, x : _?LetterQ :> x], 2]

]</lang>

<lang Mathematica>RunLengthDecode[input_List]:= ConstantArray @@@ input // Flatten // StringJoin</lang>

This second encode function is adapted from the MathWorld example.

recreates the string.

Example: For the string

⚫

<lang Mathematica>mystring="WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW";</lang>

here is the run-length encoding:

⚫

<lang Mathematica>rle = RunLengthEncode[mystring]

{{"W", 12}, {"B", 1}, {"W", 12}, {"B", 3}, {"W", 24}, {"B", 1}, {"W", 14}}</lang>