dictionary_code, an Octave code which can apply a dictionary code to a text file.
A common feature of lossless compression schemes is the construction of a "dictionary" of the symbols or words occuring in the file, and the replacement of symbols by dictionary indices.
These functions illustrate that idea, by starting with a version of the Gettysburg Address. In order to simplify our work, we remove punctuation and capitalization. Using MATLAB's "textread" function, we can create a cell array where each entry is a word in the file. Using MATLAB's unique() function we can construct a "dictionary" that lists in alphabetic order every word occurring in the file. Using a surprisingly obscure MATLAB function, we can then replace every word in the text file by its dictionary index. This is the operation of the "dictionary_encode()" function.
In order to decode or uncompress the file, we need both the encoded file and the dictionary. For our example, the dictionary is stored as a separate file, although compression schemes pack both the encoded text and the dictionary together. The function "dictionary_decode()" can then recover the original message.
The computer code and data files described and made available on this web page are distributed under the MIT license
dictionary_code is available in a MATLAB version and an Octave version.
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