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# Natural Language Toolkit: Minimal Sets
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#
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# Copyright (C) 2001-2020 NLTK Project
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# Author: Steven Bird <stevenbird1@gmail.com>
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# URL: <http://nltk.org>
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# For license information, see LICENSE.TXT
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from collections import defaultdict
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class MinimalSet(object):
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"""
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Find contexts where more than one possible target value can
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appear. E.g. if targets are word-initial letters, and contexts
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are the remainders of words, then we would like to find cases like
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"fat" vs "cat", and "training" vs "draining". If targets are
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parts-of-speech and contexts are words, then we would like to find
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cases like wind (noun) 'air in rapid motion', vs wind (verb)
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'coil, wrap'.
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"""
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def __init__(self, parameters=None):
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"""
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Create a new minimal set.
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:param parameters: The (context, target, display) tuples for the item
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:type parameters: list(tuple(str, str, str))
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"""
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self._targets = set() # the contrastive information
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self._contexts = set() # what we are controlling for
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self._seen = defaultdict(set) # to record what we have seen
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self._displays = {} # what we will display
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if parameters:
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for context, target, display in parameters:
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self.add(context, target, display)
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def add(self, context, target, display):
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"""
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Add a new item to the minimal set, having the specified
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context, target, and display form.
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:param context: The context in which the item of interest appears
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:type context: str
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:param target: The item of interest
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:type target: str
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:param display: The information to be reported for each item
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:type display: str
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"""
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# Store the set of targets that occurred in this context
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self._seen[context].add(target)
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# Keep track of which contexts and targets we have seen
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self._contexts.add(context)
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self._targets.add(target)
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# For a given context and target, store the display form
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self._displays[(context, target)] = display
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def contexts(self, minimum=2):
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"""
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Determine which contexts occurred with enough distinct targets.
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:param minimum: the minimum number of distinct target forms
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:type minimum: int
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:rtype list
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"""
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return [c for c in self._contexts if len(self._seen[c]) >= minimum]
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def display(self, context, target, default=""):
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if (context, target) in self._displays:
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return self._displays[(context, target)]
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else:
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return default
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def display_all(self, context):
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result = []
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for target in self._targets:
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x = self.display(context, target)
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if x:
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result.append(x)
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return result
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def targets(self):
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return self._targets
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