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from py_stringmatching import utils
from py_stringmatching.similarity_measure.jaro_winkler import JaroWinkler
from py_stringmatching.similarity_measure.hybrid_similarity_measure import \
HybridSimilarityMeasure
class MongeElkan(HybridSimilarityMeasure):
"""Computes Monge-Elkan measure.
The Monge-Elkan similarity measure is a type of hybrid similarity measure that combines the benefits of
sequence-based and set-based methods. This can be effective for domains in which more control is needed
over the similarity measure. It implicitly uses a secondary similarity measure, such as Levenshtein to compute
over all similarity score. See the string matching chapter in the DI book (Principles of Data Integration).
Args:
sim_func (function): Secondary similarity function. This is expected to be a sequence-based
similarity measure (defaults to Jaro-Winkler similarity measure).
Attributes:
sim_func (function): An attribute to store the secondary similarity function.
"""
def __init__(self, sim_func=JaroWinkler().get_raw_score):
self.sim_func = sim_func
super(MongeElkan, self).__init__()
def get_raw_score(self, bag1, bag2):
"""Computes the raw Monge-Elkan score between two bags (lists).
Args:
bag1,bag2 (list): Input lists.
Returns:
Monge-Elkan similarity score (float).
Raises:
TypeError : If the inputs are not lists or if one of the inputs is None.
Examples:
>>> me = MongeElkan()
>>> me.get_raw_score(['Niall'], ['Neal'])
0.8049999999999999
>>> me.get_raw_score(['Niall'], ['Nigel'])
0.7866666666666667
>>> me.get_raw_score(['Comput.', 'Sci.', 'and', 'Eng.', 'Dept.,', 'University', 'of', 'California,', 'San', 'Diego'], ['Department', 'of', 'Computer', 'Science,', 'Univ.', 'Calif.,', 'San', 'Diego'])
0.8364448130130768
>>> me.get_raw_score([''], ['a'])
0.0
>>> me = MongeElkan(sim_func=NeedlemanWunsch().get_raw_score)
>>> me.get_raw_score(['Comput.', 'Sci.', 'and', 'Eng.', 'Dept.,', 'University', 'of', 'California,', 'San', 'Diego'], ['Department', 'of', 'Computer', 'Science,', 'Univ.', 'Calif.,', 'San', 'Diego'])
2.0
>>> me = MongeElkan(sim_func=Affine().get_raw_score)
>>> me.get_raw_score(['Comput.', 'Sci.', 'and', 'Eng.', 'Dept.,', 'University', 'of', 'California,', 'San', 'Diego'], ['Department', 'of', 'Computer', 'Science,', 'Univ.', 'Calif.,', 'San', 'Diego'])
2.25
References:
* Principles of Data Integration book
"""
# input validations
utils.sim_check_for_none(bag1, bag2)
utils.sim_check_for_list_or_set_inputs(bag1, bag2)
# if exact match return 1.0
if utils.sim_check_for_exact_match(bag1, bag2):
return 1.0
# if one of the strings is empty return 0
if utils.sim_check_for_empty(bag1, bag2):
return 0
# aggregated sum of all the max sim score of all the elements in bag1
# with elements in bag2
sum_of_maxes = 0
for el1 in bag1:
max_sim = float('-inf')
for el2 in bag2:
max_sim = max(max_sim, self.sim_func(el1, el2))
sum_of_maxes += max_sim
sim = float(sum_of_maxes) / float(len(bag1))
return sim
def get_sim_func(self):
"""Get the secondary similarity function.
Returns:
secondary similarity function (function).
"""
return self.sim_func
def set_sim_func(self, sim_func):
"""Set the secondary similarity function.
Args:
sim_func (function): Secondary similarity function.
"""
self.sim_func = sim_func
return True
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