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import unittest
from nltk.metrics import (
BigramAssocMeasures,
QuadgramAssocMeasures,
TrigramAssocMeasures,
)
## Test the likelihood ratio metric
_DELTA = 1e-8
class TestLikelihoodRatio(unittest.TestCase):
def test_lr_bigram(self):
self.assertAlmostEqual(
BigramAssocMeasures.likelihood_ratio(2, (4, 4), 20),
2.4142743368419755,
delta=_DELTA,
)
self.assertAlmostEqual(
BigramAssocMeasures.likelihood_ratio(1, (1, 1), 1), 0.0, delta=_DELTA
)
self.assertRaises(
ValueError,
BigramAssocMeasures.likelihood_ratio,
*(0, (2, 2), 2),
)
def test_lr_trigram(self):
self.assertAlmostEqual(
TrigramAssocMeasures.likelihood_ratio(1, (1, 1, 1), (1, 1, 1), 2),
5.545177444479562,
delta=_DELTA,
)
self.assertAlmostEqual(
TrigramAssocMeasures.likelihood_ratio(1, (1, 1, 1), (1, 1, 1), 1),
0.0,
delta=_DELTA,
)
self.assertRaises(
ValueError,
TrigramAssocMeasures.likelihood_ratio,
*(1, (1, 1, 2), (1, 1, 2), 2),
)
def test_lr_quadgram(self):
self.assertAlmostEqual(
QuadgramAssocMeasures.likelihood_ratio(
1, (1, 1, 1, 1), (1, 1, 1, 1, 1, 1), (1, 1, 1, 1), 2
),
8.317766166719343,
delta=_DELTA,
)
self.assertAlmostEqual(
QuadgramAssocMeasures.likelihood_ratio(
1, (1, 1, 1, 1), (1, 1, 1, 1, 1, 1), (1, 1, 1, 1), 1
),
0.0,
delta=_DELTA,
)
self.assertRaises(
ValueError,
QuadgramAssocMeasures.likelihood_ratio,
*(1, (1, 1, 1, 1), (1, 1, 1, 1, 1, 2), (1, 1, 1, 1), 1),
)
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