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Jorge Castro: Getting Started working on Unity
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Text::Ngram(3pm) User Contributed Perl Documentation Text::Ngram(3pm) NAME
Text::Ngram - Ngram analysis of text SYNOPSIS
use Text::Ngram qw(ngram_counts add_to_counts); my $text = "abcdefghijklmnop"; my $hash_r = ngram_counts($text, 3); # Window size = 3 # $hash_r => { abc => 1, bcd => 1, ... } add_to_counts($more_text, 3, $hash_r); DESCRIPTION
n-Gram analysis is a field in textual analysis which uses sliding window character sequences in order to aid topic analysis, language determination and so on. The n-gram spectrum of a document can be used to compare and filter documents in multiple languages, prepare word prediction networks, and perform spelling correction. The neat thing about n-grams, though, is that they're really easy to determine. For n=3, for instance, we compute the n-gram counts like so: the cat sat on the mat --- $counts{"the"}++; --- $counts{"he "}++; --- $counts{"e c"}++; ... This module provides an efficient XS-based implementation of n-gram spectrum analysis. There are two functions which can be imported: ngram_counts This first function returns a hash reference with the n-gram histogram of the text for the given window size. The default window size is 5. $href = ngram_counts(\%config, $text, $window_size); As of version 0.14, the %config may instead be passed in as named arguments: $href = ngram_counts($text, $window_size, %config); The only necessary parameter is $text. The possible value for %config are: flankbreaks If set to 1 (default), breaks are flanked by spaces; if set to 0, they're not. Breaks are punctuation and other non-alphabetic characters, which, unless you use "punctuation => 0" in your configuration, do not make it into the returned hash. Here's an example, supposing you're using the default value for punctuation(1): my $text = "Hello, world"; my $hash = ngram_counts($text, 5); That produces the following ngrams: { 'Hello' => 1, 'ello ' => 1, ' worl' => 1, 'world' => 1, } On the other hand, this: my $text = "Hello, world"; my $hash = ngram_counts({flankbreaks => 0}, $text, 5); Produces the following ngrams: { 'Hello' => 1, ' worl' => 1, 'world' => 1, } lowercase If set to 0, casing is preserved. If set to 1, all letters are lowercased before counting ngrams. Default is 1. # Get all ngrams of size 4 preserving case $href_p = ngram_counts( {lowercase => 0}, $text, 4 ); punctuation If set to 0 (default), punctuation is removed before calculating the ngrams. Set to 1 to preserve it. # Get all ngrams of size 2 preserving punctuation $href_p = ngram_counts( {punctuation => 1}, $text, 2 ); spaces If set to 0 (default is 1), no ngrams containing spaces will be returned. # Get all ngrams of size 3 that do not contain spaces $href = ngram_counts( {spaces => 0}, $text, 3); If you're going to request both types of ngrams, than the best way to avoid calculating the same thing twice is probably this: $href_with_spaces = ngram_counts($text[, $window]); $href_no_spaces = $href_with_spaces; for (keys %$href_no_spaces) { delete $href->{$_} if / / } add_to_counts This incrementally adds to the supplied hash; if $window is zero or undefined, then the window size is computed from the hash keys. add_to_counts($more_text, $window, $href) TO DO
o Look further into the tests. Sort them and add more. SEE ALSO
Cavnar, W. B.(1993). N-gram-based text filtering for TREC-2. In D. Harman (Ed.), Proceedings of TREC-2: Text Retrieval Conference 2. Washington, DC: National Bureau of Standards. Shannon, C. E.(1951). Predication and entropy of printed English. The Bell System Technical Journal, 30. 50-64. Ullmann, J. R.(1977). Binary n-gram technique for automatic correction of substitution, deletion, insert and reversal errors in words. Computer Journal, 20. 141-147. AUTHOR
Maintained by Alberto Simoes, "ambs@cpan.org". Previously maintained by Jose Castro, "cog@cpan.org". Originally created by Simon Cozens, "simon@cpan.org". COPYRIGHT AND LICENSE
Copyright 2006 by Alberto Simoes Copyright 2004 by Jose Castro Copyright 2003 by Simon Cozens This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.14.2 2012-01-25 Text::Ngram(3pm)
