Jaro winkler

strings/jaro_winkler.py

@@ -0,0 +1,62 @@
+""" https://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance """
+import math
+
+
+def jaro_winkler(first_string: str, second_string: str) -> float:
+    """
+    Jaro–Winkler distance is a string metric measuring an edit distance between two sequences.
+    Output value is between 0.0 and 1.0.
+
+    >>> jaro_winkler("martha", "marhta")
+    0.9611111111111111
+
+    >>> jaro_winkler("CRATE", "TRACE")
+    0.6222222222222222
+
+    >>> jaro_winkler("test", "dbdbdbdb")
+    0.0
+
+    >>> jaro_winkler("test", "test")
+    1.0
+
+    >>> jaro_winkler("hello world", "HeLLo W0rlD")
+    0.5303030303030303
+
+    >>> jaro_winkler("test", "")
+    0.0
+    """
+    max_distance = math.floor(max(len(first_string), len(second_string)) / 2) - 1
+
+    # matching characters
+    match_count = 0
+    for i, c1 in enumerate(first_string):
+        for j, c2 in enumerate(second_string):
+            if c1 == c2 and abs(i - j) < max_distance:
+                match_count += 1
+
+    # transposition
+    not_match = len(
+        [(c1, c2) for c1, c2 in zip(first_string, second_string) if c1 != c2]
+    )
+
+    if not match_count:
+        jaro = 0.0
+    else:
+        jaro = 1 / 3 * (
+            match_count / len(first_string)
+            + match_count / len(second_string)
+            + (match_count - not_match / 2) / match_count)
+
+    # common prefix up to 4 characters
+    prefix_len = 0
+    for c1, c2 in zip(first_string[:4], second_string[:4]):
+        if c1 == c2:
+            prefix_len += 1
+        else:
+            break
+
+    return jaro + 0.1 * prefix_len * (1 - jaro)
+
+
+if __name__ == '__main__':
+    print(jaro_winkler("hello", "world"))