General natural language (tokenizing, stemming (English, Russian, Spanish), classification, inflection, phonetics, tfidf, WordNet, jaro-winkler, Levenshtein distance, Dice's Coefficient) facilities for node.
npm install huba-naturalnatural
=======
"Natural" is a general natural language facility for nodejs. Tokenizing,
stemming, classification, phonetics, tf-idf, WordNet, string similarity,
and some inflections are currently supported.
It's still in the early stages, so we're very interested in bug reports,
contributions and the like.
Note that many algorithms from Rob Ellis's node-nltools are
being merged into this project and will be maintained from here onward.
At the moment, most of the algorithms are English-specific, but in the long-term, some diversity
will be in order. Thanks to Polyakov Vladimir, Russian stemming has been added!, Thanks to David Przybilla, Spanish stemming has been added!.
Aside from this README, the only documentation is this DZone article and here on my blog, which is a bit older.
Installation
------------
If you're just looking to use natural without your own node application,
you can install via NPM like so:
npm install natural
If you're interested in contributing to natural, or just hacking on it, then by all
means fork away!
Tokenizers
----------
Word, Regexp, and Treebank tokenizers are provided for breaking text up into
arrays of tokens:
``javascript`
var natural = require('natural'),
tokenizer = new natural.WordTokenizer();
console.log(tokenizer.tokenize("your dog has fleas."));
// [ 'your', 'dog', 'has', 'fleas' ]
The other tokenizers follow a similar pattern:
`javascript
tokenizer = new natural.TreebankWordTokenizer();
console.log(tokenizer.tokenize("my dog hasn't any fleas."));
// [ 'my', 'dog', 'has', 'n\'t', 'any', 'fleas', '.' ]
tokenizer = new natural.RegexpTokenizer({pattern: /\-/});
console.log(tokenizer.tokenize("flea-dog"));
// [ 'flea', 'dog' ]
tokenizer = new natural.WordPunctTokenizer();
console.log(tokenizer.tokenize("my dog hasn't any fleas."));
// [ 'my', 'dog', 'hasn', '\'', 't', 'any', 'fleas', '.' ]
`
String Distance
----------------------
Natural provides an implementation of the Jaro–Winkler string distance measuring algorithm.
This will return a number between 0 and 1 which tells how closely the strings match (0 = not at all, 1 = exact match):
`javascript`
var natural = require('natural');
console.log(natural.JaroWinklerDistance("dixon","dicksonx"))
console.log(natural.JaroWinklerDistance('not', 'same'));
Output:
`javascript`
0.7466666666666666
0
Natural also offers support for Levenshtein distances:
`javascript`
var natural = require('natural');
console.log(natural.LevenshteinDistance("ones","onez"));
console.log(natural.LevenshteinDistance('one', 'one'));
Output:
`javascript`
1
0
The cost of the three edit operations are modifiable for Levenshtein:
`javascript`
console.log(natural.LevenshteinDistance("ones","onez", {
insertion_cost: 1,
deletion_cost: 1,
substitution_cost: 1
}));
Output:
`javascript`
1
And Dice's co-efficient:
`javascript`
var natural = require('natural');
console.log(natural.DiceCoefficient('thing', 'thing'));
console.log(natural.DiceCoefficient('not', 'same'));
Output:
`javascript`
1
0
Stemmers
--------
Currently stemming is supported via the Porter and Lancaster (Paice/Husk) algorithms.
`javascript`
var natural = require('natural');
This example uses a Porter stemmer. "word" is returned.
`javascript`
console.log(natural.PorterStemmer.stem("words")); // stem a single word
in Russian:
`javascript`
console.log(natural.PorterStemmerRu.stem("падший"));
in Spanish:
`javascript`
console.log(natural.PorterStemmerEs.stem("jugaría"));
attach() patches stem() and tokenizeAndStem() to String as a shortcut toPorterStemmer.stem(token). tokenizeAndStem() breaks text up into single words
and returns an array of stemmed tokens.
`javascript`
natural.PorterStemmer.attach();
console.log("i am waking up to the sounds of chainsaws".tokenizeAndStem());
console.log("chainsaws".stem());
the same thing can be done with a Lancaster stemmer:
`javascript`
natural.LancasterStemmer.attach();
console.log("i am waking up to the sounds of chainsaws".tokenizeAndStem());
console.log("chainsaws".stem());
Classifiers
----------------------
Two classifiers are currently supported, Naive Bayes and logistic regression.
The following examples use the BayesClassifier class, but the
LogisticRegressionClassifier class could be substituted instead.
`javascript`
var natural = require('natural'),
classifier = new natural.BayesClassifier();
You can train the classifier on sample text. It will use reasonable defaults to
tokenize and stem the text.
`javascript
classifier.addDocument('i am long qqqq', 'buy');
classifier.addDocument('buy the q\'s', 'buy');
classifier.addDocument('short gold', 'sell');
classifier.addDocument('sell gold', 'sell');
classifier.train();
`
Outputs "sell"
`javascript`
console.log(classifier.classify('i am short silver'));
Outputs "buy"
`javascript`
console.log(classifier.classify('i am long copper'));
You have access to the set of matched classes and the associated value from the classifier.
Outputs:
`javascript`
[ { label: 'buy', value: 0.39999999999999997 },
{ label: 'sell', value: 0.19999999999999998 } ]
From this:
`javascript`
console.log(classifier.getClassifications('i am long copper'));
The classifier can also be trained with and can classify arrays of tokens, strings, or
any mixture of the two. Arrays let you use entirely custom data with your own
tokenization/stemming, if you choose to implement it.
`javascript`
classifier.addDocument(['sell', 'gold'], 'sell');
The training process can be monitored by subscribing to the event trainedWithDocument that's emitted by the classifier, this event's emitted each time a document is finished being trained against:
classifier.events.on('trainedWithDocument', function (obj) {
console.log(obj);
/* {
* total: 23 // There are 23 total documents being trained against
* index: 12 // The index/number of the document that's just been trained against
* doc: {...} // The document that has just been indexed
* }
*/
});
A classifier can also be persisted and recalled so you can reuse a training
`javascript`
classifier.save('classifier.json', function(err, classifier) {
// the classifier is saved to the classifier.json file!
});
To recall from the classifier.json saved above:
`javascript`
natural.BayesClassifier.load('classifier.json', null, function(err, classifier) {
console.log(classifier.classify('long SUNW'));
console.log(classifier.classify('short SUNW'));
});
A classifier can also be serialized and deserialized like so:
`javascript
var classifier = new natural.BayesClassifier();
classifier.addDocument(['sell', 'gold'], 'sell');
classifier.addDocument(['buy', 'silver'], 'buy');
// serialize
var raw = JSON.stringify(classifier);
// deserialize
var restoredClassifier = natural.BayesClassifier.restore(JSON.parse(raw));
console.log(restoredClassifier.classify('i should sell that'));
`
Phonetics
---------
Phonetic matching (sounds-like) matching can be done with the SoundEx,
Metaphone or DoubleMetaphone algorithms
`javascript
var natural = require('natural'),
metaphone = natural.Metaphone, soundEx = natural.SoundEx;
var wordA = 'phonetics';
var wordB = 'fonetix';
`
To test the two words to see if they sound alike:
`javascript`
if(metaphone.compare(wordA, wordB))
console.log('they sound alike!');
The raw phonetics are obtained with process():
`javascript`
console.log(metaphone.process('phonetics'));
A maximum code length can be supplied:
`javascript`
console.log(metaphone.process('phonetics', 3));
DoubleMetaphone deals with two encodings returned in an array. This
feature is experimental and subject to change:
`javascript
var natural = require('natural'),
dm = natural.DoubleMetaphone;
var encodings = dm.process('Matrix');
console.log(encodings[0]);
console.log(encodings[1]);
`
Attaching will patch String with useful methods:
`javascript`
metaphone.attach();
soundsLike is essentially a shortcut to Metaphone.compare:
`javascript`
if(wordA.soundsLike(wordB))
console.log('they sound alike!');
The raw phonetics are obtained with phonetics():
`javascript`
console.log('phonetics'.phonetics());
Full text strings can be tokenized into arrays of phonetics (much like how tokenization-to-arrays works for stemmers):
`javascript`
console.log('phonetics rock'.tokenizeAndPhoneticize());
Same module operations applied with SoundEx:
`javascript`
if(soundEx.compare(wordA, wordB))
console.log('they sound alike!');
The same String patches apply with soundEx:
`javascript
soundEx.attach();
if(wordA.soundsLike(wordB))
console.log('they sound alike!');
console.log('phonetics'.phonetics());
`
Inflectors
----------
Nouns can be pluralized/singularized with a NounInflector:
`javascript`
var natural = require('natural'),
nounInflector = new natural.NounInflector();
To pluralize a word (outputs "radii"):
`javascript`
console.log(nounInflector.pluralize('radius'));
To singularize a word (outputs "beer"):
`javascript`
console.log(nounInflector.singularize('beers'));
Like many of the other features, String can be patched to perform the operations
directly. The "Noun" suffix on the methods is necessary, as verbs will be
supported in the future.
`javascript`
nounInflector.attach();
console.log('radius'.pluralizeNoun());
console.log('beers'.singularizeNoun());
Numbers can be counted with a CountInflector:
`javascript`
var countInflector = natural.CountInflector;
Outputs "1st":
`javascript`
console.log(countInflector.nth(1));
Outputs "111th":
`javascript`
console.log(countInflector.nth(111));
Present Tense Verbs can be pluralized/singularized with a PresentVerbInflector.
This feature is still experimental as of 0.0.42, so use with caution, and please
provide feedback.
`javascript`
var verbInflector = new natural.PresentVerbInflector();
Outputs "becomes":
`javascript`
console.log(verbInflector.singularize('become'));
Outputs "become":
`javascript`
console.log(verbInflector.pluralize('becomes'));
Like many other natural modules, attach() can be used to patch strings with
handy methods.
`javascript`
verbInflector.attach();
console.log('walk'.singularizePresentVerb());
console.log('walks'.pluralizePresentVerb());
N-Grams
-------
n-grams can be obtained for either arrays or strings (which will be tokenized
for you):
`javascript`
var NGrams = natural.NGrams;
`javascript`
console.log(NGrams.bigrams('some words here'));
console.log(NGrams.bigrams(['some', 'words', 'here']));
Both of the above output: [ [ 'some', 'words' ], [ 'words', 'here' ] ]
`javascript`
console.log(NGrams.trigrams('some other words here'));
console.log(NGrams.trigrams(['some', 'other', 'words', 'here']));
Both of the above output: [ [ 'some', 'other', 'words' ],
[ 'other', 'words', 'here' ] ]
`javascript`
console.log(NGrams.ngrams('some other words here for you', 4));
console.log(NGrams.ngrams(['some', 'other', 'words', 'here', 'for',
'you'], 4));
The above outputs: [ [ 'some', 'other', 'words', 'here' ],
[ 'other', 'words', 'here', 'for' ],
[ 'words', 'here', 'for', 'you' ] ]
n-grams can also be returned with left or right padding by passing a start and/or end symbol to the bigrams, trigrams or ngrams.
`javascript`
console.log(NGrams.ngrams('some other words here for you', 4, '[start]', '[end]'));
The above will output:
`
[ [ '[start]', '[start]', '[start]', 'some' ],
[ '[start]', '[start]', 'some', 'other' ],
[ '[start]', 'some', 'other', 'words' ],
[ 'some', 'other', 'words', 'here' ],
[ 'other', 'words', 'here', 'for' ],
[ 'words', 'here', 'for', 'you' ],
[ 'here', 'for', 'you', '[end]' ],
[ 'for', 'you', '[end]', '[end]' ],
[ 'you', '[end]', '[end]', '[end]' ] ]
For only end symbols, pass null for the start symbol, for instance:`javascript`
console.log(NGrams.ngrams('some other words here for you', 4, null, '[end]'));
Will output:
`
[ [ 'some', 'other', 'words', 'here' ],
[ 'other', 'words', 'here', 'for' ],
[ 'words', 'here', 'for', 'you' ],
[ 'here', 'for', 'you', '[end]' ],
[ 'for', 'you', '[end]', '[end]' ],
[ 'you', '[end]', '[end]', '[end]' ] ]
For Chinese like languages, you can use NGramsZH to do a n-gram, and all apis are the same:
`javascript`
var NGramsZH = natural.NGramsZH;
console.log(NGramsZH.bigrams('中文测试'));
console.log(NGramsZH.bigrams(['中', '文', '测', '试']));
console.log(NGramsZH.trigrams('中文测试'));
console.log(NGramsZH.trigrams(['中', '文', '测', '试']));
console.log(NGramsZH.ngrams('一个中文测试', 4));
console.log(NGramsZH.ngrams(['一', '个', '中', '文', '测',
'试'], 4));
tf-idf
-----
Term Frequency–Inverse Document Frequency (tf-idf) is implemented to determine how important a word (or words) is to a
document relative to a corpus. The following example will add four documents to
a corpus and determine the weight of the word "node" and then the weight of the
word "ruby" in each document.
`javascript
var natural = require('natural'),
TfIdf = natural.TfIdf,
tfidf = new TfIdf();
tfidf.addDocument('this document is about node.');
tfidf.addDocument('this document is about ruby.');
tfidf.addDocument('this document is about ruby and node.');
tfidf.addDocument('this document is about node. it has node examples');
console.log('node --------------------------------');
tfidf.tfidfs('node', function(i, measure) {
console.log('document #' + i + ' is ' + measure);
});
console.log('ruby --------------------------------');
tfidf.tfidfs('ruby', function(i, measure) {
console.log('document #' + i + ' is ' + measure);
});
`
The above outputs:
`
node --------------------------------
document #0 is 1.4469189829363254
document #1 is 0
document #2 is 1.4469189829363254
document #3 is 2.8938379658726507
ruby --------------------------------
document #0 is 0
document #1 is 1.466337068793427
document #2 is 1.466337068793427
document #3 is 0
This approach can also be applied to individual documents.
The following example measures the term "node" in the first and second documents.
`javascript`
console.log(tfidf.tfidf('node', 0));
console.log(tfidf.tfidf('node', 1));
A TfIdf instance can also load documents from files on disk.
`javascript`
var tfidf = new TfIdf();
tfidf.addFileSync('data_files/one.txt');
tfidf.addFileSync('data_files/two.txt');
Multiple terms can be measured as well, with their weights being added into
a single measure value. The following example determines that the last document
is the most relevant to the words "node" and "ruby".
`javascript
var natural = require('natural'),
TfIdf = natural.TfIdf,
tfidf = new TfIdf();
tfidf.addDocument('this document is about node.');
tfidf.addDocument('this document is about ruby.');
tfidf.addDocument('this document is about ruby and node.');
tfidf.tfidfs('node ruby', function(i, measure) {
console.log('document #' + i + ' is ' + measure);
});
`
The above outputs:
`
document #0 is 1.2039728043259361
document #1 is 1.2039728043259361
document #2 is 2.4079456086518722
The examples above all use strings, which case natural to automatically tokenize the input.
If you wish to perform your own tokenization or other kinds of processing, you
can do so, then pass in the resultant arrays later. This approach allows you to bypass natural's
default preprocessing.
`javascript
var natural = require('natural'),
TfIdf = natural.TfIdf,
tfidf = new TfIdf();
tfidf.addDocument(['document', 'about', 'node']);
tfidf.addDocument(['document', 'about', 'ruby']);
tfidf.addDocument(['document', 'about', 'ruby', 'node']);
tfidf.addDocument(['document', 'about', 'node', 'node', 'examples']);
tfidf.tfidfs(['node', 'ruby'], function(i, measure) {
console.log('document #' + i + ' is ' + measure);
});
`
It's possible to retrieve a list of all terms in a document, sorted by their
importance.
`javascript`
tfidf.listTerms(0 /document index/).forEach(function(item) {
console.log(item.term + ': ' + item.tfidf);
});
A TfIdf instance can also be serialized and deserialized for save and recall.
`javascript
var tfidf = new TfIdf();
tfidf.addDocument('document one', 'un');
tfidf.addDocument('document Two', 'deux');
var s = JSON.stringify(tfidf);
// save "s" to disk, database or otherwise
// assuming you pulled "s" back out of storage.
var tfidf = new TfIdf(JSON.parse(s));
`
Tries
-----
Tries are a very efficient data structure used for prefix-based searches.
Natural comes packaged with a basic Trie implementation which can support match collection along a path,
existence search and prefix search.
You need to add words to build up the dictionary of the Trie, this is an example of basic Trie set up:
`javascript
var natural = require('natural'),
Trie = natural.Trie;
var trie = new Trie();
// Add one string at a time
trie.addString("test");
// Or add many strings
trie.addStrings(["string1", "string2", "string3"]);
`
#### Contains
The most basic operation on a Trie is to see if a search string is marked as a word in the Trie.
`javascript`
console.log(trie.contains("test")); // true
console.log(trie.contains("asdf")); // false
The find prefix search will find the longest prefix that is identified as a word in the trie.
It will also return the remaining portion of the string which it was not able to match.
`javascript`
console.log(trie.findPrefix("tester")); // ['test', 'er']
console.log(trie.findPrefix("string4")); // [null, '4']
console.log(trie.findPrefix("string3")); // ['string3', '']
This search will return all prefix matches along the search string path.
`javascript`
trie.addString("tes");
trie.addString("est");
console.log(trie.findMatchesOnPath("tester")); // ['tes', 'test'];
This search will return all of the words in the Trie with the given prefix, or [ ] if not found.
`javascript`
console.log(trie.keysWithPrefix("string")); // ["string1", "string2", "string3"]
By default the trie is case-sensitive, you can use it in case-_in_sensitive mode by passing false
to the Trie constructor.
`javascript
trie.contains("TEST"); // false
var ciTrie = new Trie(false);
ciTrie.addString("test");
ciTrie.contains("TEsT"); // true
`
In the case of the searches which return strings, all strings returned will be in lower case if you are in case-_in_sensitive mode.
EdgeWeightedDigraph
-------------------
EdgeWeightedDigraph represents a digraph, you can add an edge, get the number vertexes, edges, get all edges and use toString to print the Digraph.
initialize a digraph:
`javascript`
var EdgeWeightedDigraph = natural.EdgeWeightedDigraph;
var digraph = new EdgeWeightedDigraph();
digraph.add(5,4,0.35);
digraph.add(5,1,0.32);
digraph.add(1,3,0.29);
digraph.add(6,2,0.40);
digraph.add(3,6,0.52);
digraph.add(6,4,0.93);
the api used is: add(from, to, weight).
get the number of vertexes:
`javascript`
console.log(digraph.v());
you will get 5.
get the number of edges:
`javascript`
console.log(digraph.e());
you will get 5.
ShortestPathTree
----------------
ShortestPathTree represents a data type for solving the single-source shortest paths problem in
edge-weighted directed acyclic graphs (DAGs).
The edge weights can be positive, negative, or zero. There are three APIs:
getDistTo(vertex),
hasPathTo(vertex),
pathTo(vertex).
`javascript`
var ShortestPathTree = natural.ShortestPathTree;
var spt = new ShortestPathTree(digraph, 5);
digraph is an instance of EdgeWeightedDigraph, the second param is the start vertex of DAG.
Will return the dist to vertex.
`javascript`
console.log(spt.getDistTo(4));
the output will be: 0.35
`javascript`
console.log(spt.hasDistTo(4));
console.log(spt.hasDistTo(5));
output will be:
`javascript`
true
false
`javascript`
console.log(spt.pathTo(4));
output will be:
`javascript`
[5, 4]
LongestPathTree
----------------
LongestPathTree represents a data type for solving the single-source shortest paths problem in
edge-weighted directed acyclic graphs (DAGs).
The edge weights can be positive, negative, or zero. There are three APIs same as ShortestPathTree:
getDistTo(vertex),
hasPathTo(vertex),
pathTo(vertex).
`javascript`
var ShortestPathTree = natural.ShortestPathTree;
var spt = new ShortestPathTree(digraph, 5);
digraph is an instance of EdgeWeightedDigraph, the second param is the start vertex of DAG.
Will return the dist to vertex.
`javascript`
console.log(spt.getDistTo(4));
the output will be: 2.06
`javascript`
console.log(spt.hasDistTo(4));
console.log(spt.hasDistTo(5));
output will be:
`javascript`
true
false
`javascript`
console.log(spt.pathTo(4));
output will be:
`javascript`
[5, 1, 3, 6, 4]
WordNet
-------
One of the newest and most experimental features in natural is WordNet integration. Here's an
example of using natural to look up definitions of the word node. To use the WordNet module,
first install the WordNet database files using the WNdb module:
npm install WNdb
(For node < v0.6, please use 'npm install WNdb@3.0.0')
Keep in mind that the WordNet integration is to be considered experimental at this point,
and not production-ready. The API is also subject to change.
Here's an example of looking up definitions for the word, "node".
`javascript
var wordnet = new natural.WordNet();
wordnet.lookup('node', function(results) {
results.forEach(function(result) {
console.log('------------------------------------');
console.log(result.synsetOffset);
console.log(result.pos);
console.log(result.lemma);
console.log(result.synonyms);
console.log(result.pos);
console.log(result.gloss);
});
});
`
Given a synset offset and a part of speech, a definition can be looked up directly.
`javascript
var wordnet = new natural.WordNet();
wordnet.get(4424418, 'n', function(result) {
console.log('------------------------------------');
console.log(result.lemma);
console.log(result.pos);
console.log(result.gloss);
console.log(result.synonyms);
});
`
If you have _manually_ downloaded the WordNet database files, you can pass the folder to the constructor:
`javascript`
var wordnet = new natural.WordNet('/my/wordnet/dict');
As of v0.1.11, WordNet data files are no longer automatically downloaded.
Princeton University "About WordNet." WordNet. Princeton University. 2010.
Spellcheck
------------
A probabilistic spellchecker based on http://norvig.com/spell-correct.html
This is best constructed with an array of tokens from a corpus, but a simple list of words from a dictionary will work.
`javascript`
var corpus = ['something', 'soothing'];
var spellcheck = new Spellcheck(corpus);
It uses the trie datastructure for fast boolean lookup of a word
`javascript`
spellcheck.isCorrect('cat'); // false
It suggests corrections (sorted by probability in descending order) that are up to a maximum edit distance away from the input word. According to Norvig, a max distance of 1 will cover 80% to 95% of spelling mistakes. After a distance of 2, it becomes very slow.
`javascript`
spellcheck.getCorrections('soemthing', 1); // ['something']
spellcheck.getCorrections('soemthing', 2); // ['something', 'soothing']
POS Tagger
-----------
This is a part-of-speech tagger based on Eric Brill's transformational
algorithm. Transformation rules are specified in external files.
javascript
var Tagger = require("./lib/natural").BrillPOSTagger;var base_folder = "some_path/lib/natural/brill_pos_tagger";
var rules_file = base_folder + "/data/tr_from_posjs.txt";
var lexicon_file = base_folder + "/data/lexicon_from_posjs.json";
var default_category = 'N';
var tagger = new Tagger(lexicon_file, rules_file, default_category, function(error) {
if (error) {
console.log(error);
}
else {
var sentence = ["I", "see", "the", "man", "with", "the", "telescope"];
console.log(JSON.stringify(tagger.tag(sentence)));
}
});
`$3
The lexicon is either a JSON file that has the following structure:
javascript
{
"word1": ["cat1"],
"word2": ["cat2", "cat3"],
...
}
`
or a text file:
word1 cat1 cat2
word2 cat3
...
Words may have multiple categories in the lexicon file. The tagger uses only
the first category specified.$3
Transformation rules are specified as follows:
OLD_CAT NEW_CAT PREDICATE PARAMETER
This means that if the category of the current position is OLD_CAT and the predicate is true, the category is replaced by NEW_CAT. The predicate
may use the parameter in different ways: sometimes the parameter is used for
specifying the outcome of the predicate:
NN CD CURRENT-WORD-IS-NUMBER YES
This means that if the outcome of predicate CURRENT-WORD-IS-NUMBER is YES, the
category is replaced by CD.
The parameter can also be used to check the category of a word in the sentence:
VBD NN PREV-TAG DT
Here the category of the previous word must be DT for the rule to be applied.$3
The tagger applies transformation rules that may change the category of words. The input sentence must be split into words which are assigned with categories. The tagged sentence is then processed from left to right. At each step all rules are applied once; rules are applied in the order in which they are specified. Algorithm:
javascript
function(sentence) {
var tagged_sentence = new Array(sentence.length); // snip
// Apply transformation rules
for (var i = 0, size = sentence.length; i < size; i++) {
this.transformation_rules.forEach(function(rule) {
rule.apply(tagged_sentence, i);
});
}
return(tagged_sentence);
}
`$3
Predicates are defined in module lib/Predicate.js. In that file
a function must be created that serves as predicate. A predicate accepts a
tagged sentence, the current position in the sentence that should be tagged, and
the
outcome(s) of the predicate. An example of a predicate that checks the category of the current word:
javascript
function current_word_is_tag(tagged_sentence, i, parameter) {
return(tagged_sentence[i][0] === parameter);
}
`
Some predicates accept two parameters. Next step is to map a keyword to this predicate so that it can be used in the transformation rules. The mapping is also defined in lib/Predicate.js:
javascript
var predicates = {
"CURRENT-WORD-IS-TAG": current_word_is_tag,
"PREV-WORD-IS-CAP": prev_word_is_cap
}
``Development
-----------
When developing, please:
+ Write unit tests
+ Make sure your unit tests pass
The current configuration of the unit tests requires the following environment variable to be set:
export NODE_PATH=.
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