Initial upload

Author: chuanconggao

README.md

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+The shortest yet efficient PrefixSpan implemenation in Python 3, in only 20 lines in core part.
+
+# Usage
+Just replace the variable db with your own sequences, and variable minsup with your own minimum support threshold.
+
+# Features
+Based on state-of-the-art [PrefixSpan](http://www.cs.sfu.ca/~jpei/publications/span.pdf) algorithm.

prefixspan.py

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+#! /usr/bin/env python3
+
+from collections import defaultdict
+
+db = [
+    [0, 1, 2, 3, 4],
+    [1, 1, 1, 3, 4],
+    [2, 1, 2, 2, 0],
+    [1, 1, 1, 2, 2],
+]
+
+minsup = 2
+
+results = []
+
+def mine_rec(patt, mdb):
+    def localOccurs(mdb):
+        occurs = defaultdict(list)
+
+        for (i, stoppos) in mdb:
+            seq = db[i]
+            for j in range(stoppos, len(seq)):
+                l = occurs[seq[j]]
+                if len(l) == 0 or l[-1][0] != i:
+                    l.append((i, j + 1))
+
+        return occurs
+
+    for (c, newmdb) in localOccurs(mdb).items():
+        newsup = len(newmdb)
+
+        if newsup >= minsup:
+            newpatt = patt + [c]
+
+            results.append((newpatt, [i for (i, stoppos) in newmdb]))
+            mine_rec(newpatt, newmdb)
+
+mine_rec([], [(i, 0) for i in range(len(db))])
+
+print(results)