Adding fog.metrics.overlap_coefficient. cc @diegantobass

fog/metrics/__init__.py

@@ -7,3 +7,4 @@ from fog.metrics.jaccard import (
     jaccard_similarity,
     weighted_jaccard_similarity
 )
+from fog.metrics.overlap import overlap_coefficient

fog/metrics/overlap.py

@@ -0,0 +1,52 @@
+# =============================================================================
+# Fog Overlap Coefficient
+# =============================================================================
+#
+# Functions computing the overlap coefficient.
+#
+# [Urls]:
+# https://en.wikipedia.org/wiki/Overlap_coefficient
+#
+
+ACCEPTABLE_TYPES = (set, frozenset, dict)
+
+
+def overlap_coefficient(A, B):
+    """
+    Function computing the overlap coefficient of the given sets, i.e. the size
+    of their intersection divided by the size of the smallest set.
+
+    Runs in O(n), n being the size of the smallest set.
+
+    Args:
+        A (iterable): First sequence.
+        B (iterable): Second sequence.
+
+    Returns:
+        float: overlap coefficient between A & B.
+
+    """
+    if A is B:
+        return 1.0
+
+    if not isinstance(A, ACCEPTABLE_TYPES):
+        A = set(A)
+
+    if not isinstance(B, ACCEPTABLE_TYPES):
+        B = set(B)
+
+    if len(A) == 0 or len(B) == 0:
+        return 0.0
+
+    # Swapping to iterate over smaller set and minimize lookups
+    if len(A) > len(B):
+        A, B = B, A
+
+    # Counting intersection
+    I = 0
+
+    for v in A:
+        if v in B:
+            I += 1
+
+    return I / min(len(A), len(B))

test/metrics/overlap_test.py

@@ -0,0 +1,22 @@
+# =============================================================================
+# Fog Overlap Coefficient Unit Tests
+# =============================================================================
+from pytest import approx
+from fog.metrics import overlap_coefficient
+
+TESTS = [
+    ('abc', 'abc', 1.0),
+    ('abc', 'def', 0.0),
+    ('abc', 'abd', 2 / 3),
+    ('abc', 'abcde', 1),
+    ('abcdefij', 'abc', 1),
+    (list('abcdefij'), list('abc'), 1),
+    ((1, 2, 3), (1, 2), 1),
+    ('aaaaaaabc', 'aaabbbbbbc', 1.0)
+]
+
+
+class TestOverlapCoefficient(object):
+    def test_basics(self):
+        for A, B, coefficient in TESTS:
+            assert overlap_coefficient(A, B) == coefficient