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on_match is now the second positional argument, to easily allow a variable number of patterns while keeping the method clean and readable.
218 lines
8.3 KiB
Plaintext
218 lines
8.3 KiB
Plaintext
//- 💫 DOCS > USAGE > RULE-BASED MATCHING
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include ../../_includes/_mixins
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p
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| spaCy features a rule-matching engine that operates over tokens, similar
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| to regular expressions. The rules can refer to token annotations (e.g.
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| the token #[code text] or #[code tag_], and flags (e.g. #[code IS_PUNCT]).
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| The rule matcher also lets you pass in a custom callback
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| to act on matches – for example, to merge entities and apply custom labels.
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| You can also associate patterns with entity IDs, to allow some basic
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| entity linking or disambiguation.
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+aside("What about \"real\" regular expressions?")
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+h(2, "adding-patterns") Adding patterns
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p
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| Let's say we want to enable spaCy to find a combination of three tokens:
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+list("numbers")
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+item
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| A token whose #[strong lower-case form matches "hello"], e.g. "Hello"
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| or "HELLO".
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+item
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| A token whose #[strong #[code is_punct] flag is set to #[code True]],
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| i.e. any punctuation.
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+item
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| A token whose #[strong lower-case form matches "world"], e.g. "World"
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| or "WORLD".
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+code.
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[{LOWER: 'hello'}, {IS_PUNCT: True}, {LOWER: 'world'}]
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p
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| First, we initialise the #[code Matcher] with a vocab. The matcher must
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| always share the same vocab with the documents it will operate on. We
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| can now call #[+api("matcher#add") #[code matcher.add()]] with an ID and
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| our custom pattern. The second argument lets you pass in an optional
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| callback function to invoke on a successful match. For now, we set it
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| to #[code None].
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+code.
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import spacy
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from spacy.matcher import Matcher
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from spacy.attrs import LOWER, IS_PUNCT # don't forget to import the attrs!
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nlp = spacy.load('en')
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matcher = Matcher(nlp.vocab)
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# add match ID "HelloWorld" with no callback and one pattern
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matcher.add('HelloWorld', on_match=None,
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[{LOWER: 'hello'}, {IS_PUNCT: True}, {LOWER: 'world'}])
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doc = nlp(u'Hello, world! Hello world!')
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matches = matcher(doc)
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p
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| The matcher returns a list of #[code (match_id, start, end)] tuples – in
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| this case, #[code [('HelloWorld', 0, 2)]], which maps to the span
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| #[code doc[0:2]] of our original document. Optionally, we could also
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| choose to add more than one pattern, for example to also match sequences
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| without punctuation between "hello" and "world":
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+code.
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matcher.add('HelloWorld', on_match=None,
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[{LOWER: 'hello'}, {IS_PUNCT: True}, {LOWER: 'world'}],
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[{LOWER: 'hello'}, {LOWER: 'world'}])
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p
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| By default, the matcher will only return the matches and
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| #[strong not do anything else], like merge entities or assign labels.
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| This is all up to you and can be defined individually for each pattern,
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| by passing in a callback function as the #[code on_match] argument on
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| #[code add()]. This is useful, because it lets you write entirely custom
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| and #[strong pattern-specific logic]. For example, you might want to
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| merge #[em some] patterns into one token, while adding entity labels for
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| other pattern types. You shouldn't have to create different matchers for
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| each of those processes.
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+h(2, "on_match") Adding #[code on_match] rules
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p
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| To move on to a more realistic example, let's say you're working with a
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| large corpus of blog articles, and you want to match all mentions of
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| "Google I/O" (which spaCy tokenizes as #[code ['Google', 'I', '/', 'O']]).
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| To be safe, you only match on the uppercase versions, in case someone has
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| written it as "Google i/o". You also add a second pattern with an added
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| #[code {IS_DIGIT: True}] token – this will make sure you also match on
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| "Google I/O 2017". If your pattern matches, spaCy should execute your
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| custom callback function #[code add_event_ent].
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+code.
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import spacy
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from spacy.matcher import Matcher
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from spacy.attrs import ORTH, UPPER, LOWER, IS_DIGIT
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nlp = spacy.load('en')
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matcher = Matcher(nlp.vocab)
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matcher.add('GoogleIO', on_match=add_event_ent,
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[{ORTH: 'Google'}, {UPPER: 'I'}, {ORTH: '/'}, {UPPER: 'O'}],
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[{ORTH: 'Google'}, {UPPER: 'I'}, {ORTH: '/'}, {UPPER: 'O'}, {IS_DIGIT: True}])
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# Get the ID of the 'EVENT' entity type. This is required to set an entity.
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EVENT = nlp.vocab.strings['EVENT']
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def add_event_ent(matcher, doc, i, matches):
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# Get the current match and create tuple of entity label, start and end.
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# Append entity to the doc's entity. (Don't overwrite doc.ents!)
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match_id, start, end = matches[i]
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doc.ents += ((EVENT, start, end),)
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p
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| In addition to mentions of "Google I/O", your data also contains some
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| annoying pre-processing artefacts, like leftover HTML line breaks
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| (e.g. #[code <br>] or #[code <BR/>]). While you're at it,
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| you want to merge those into one token and flag them, to make sure you
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| can easily ignore them later. So you add a second pattern and pass in a
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| function #[code merge_and_flag]:
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+code.
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matcher.add('BAD_HTML', on_match=merge_and_flag,
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[{ORTH: '<'}, {LOWER: 'br'}, {ORTH: '>'}],
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[{ORTH: '<'}, {LOWER: 'br/'}, {ORTH: '>'}])
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# Add a new custom flag to the vocab, which is always False by default.
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# BAD_HTML_FLAG will be the flag ID, which we can use to set it to True on the span.
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BAD_HTML_FLAG = doc.vocab.add_flag(lambda text: False)
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def merge_and_flag(matcher, doc, i, matches):
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match_id, start, end = matches[i]
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span = doc[start : end]
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span.merge(is_stop=True) # merge (and mark it as a stop word, just in case)
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span.set_flag(BAD_HTML_FLAG, True) # set BAD_HTML_FLAG
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+aside("Tip: Visualizing matches")
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| When working with entities, you can use #[+api("displacy") displaCy]
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| to quickly generate a NER visualization from your updated #[code Doc],
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| which can be exported as an HTML file:
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+code.o-no-block.
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from spacy import displacy
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html = displacy.render(doc, style='ent', page=True,
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options={'ents': ['EVENT']})
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| For more info and examples, see the usage workflow on
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| #[+a("/docs/usage/visualizers") visualizing spaCy].
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p
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| We can now call the matcher on our documents. The patterns will be
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| matched in the order they occur in the text.
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+code.
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doc = nlp(LOTS_OF_TEXT)
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matcher(doc)
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+h(3, "on_match-callback") The callback function
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p
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| The matcher will first collect all matches over the document. It will
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| then iterate over the matches, lookup the callback for the entity ID
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| that was matched, and invoke it. When the callback is invoked, it is
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| passed four arguments: the matcher itself, the document, the position of
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| the current match, and the total list of matches. This allows you to
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| write callbacks that consider the entire set of matched phrases, so that
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| you can resolve overlaps and other conflicts in whatever way you prefer.
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+table(["Argument", "Type", "Description"])
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+row
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+cell #[code matcher]
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+cell #[code Matcher]
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+cell The matcher instance.
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+row
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+cell #[code doc]
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+cell #[code Doc]
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+cell The document the matcher was used on.
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+row
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+cell #[code i]
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+cell int
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+cell Index of the current match (#[code matches[i]]).
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+row
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+cell #[code matches]
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+cell list
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+cell
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| A list of #[code (match_id, start, end)] tuples, describing the
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| matches. A match tuple describes a span #[code doc[start:end]].
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| The #[code match_id] is the ID of the added match pattern.
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+h(2, "quantifiers") Using quantifiers
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+table([ "Name", "Description", "Example"])
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+row
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+cell #[code !]
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+cell match exactly 0 times
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+cell negation
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+row
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+cell #[code *]
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+cell match 0 or more times
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+cell optional, variable number
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+row
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+cell #[code +]
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+cell match 1 or more times
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+cell mandatory, variable number
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+row
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+cell #[code ?]
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+cell match 0 or 1 times
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+cell optional, max one
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p
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| There are no nested or scoped quantifiers. You can build those
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| behaviours with #[code on_match] callbacks.
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