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+#!/usr/bin/env python
+
+# TASK #2 > Hash Join
+# Submitted by: Mohammad S Anwar
+# Write a script to implement Hash Join algorithm as suggested
+# by wikipedia.
+# 
+# 1. For each tuple r in the build input R
+#     1.1 Add r to the in-memory hash table
+#     1.2 If the size of the hash table equals the maximum
+#         in-memory size:
+#         1.2.1 Scan the probe input S, and add matching join
+#               tuples to the output relation
+#         1.2.2 Reset the hash table, and continue scanning the
+#               build input R
+# 2. Do a final scan of the probe input S and add the resulting
+#    join tuples to the output relation
+# Example
+# Input:
+# 
+#     @player_ages = (
+#         [20, "Alex"  ],
+#         [28, "Joe"   ],
+#         [38, "Mike"  ],
+#         [18, "Alex"  ],
+#         [25, "David" ],
+#         [18, "Simon" ],
+#     );
+# 
+#     @player_names = (
+#         ["Alex", "Stewart"],
+#         ["Joe",  "Root"   ],
+#         ["Mike", "Gatting"],
+#         ["Joe",  "Blog"   ],
+#         ["Alex", "Jones"  ],
+#         ["Simon","Duane"  ],
+#     );
+# 
+# Output:
+# 
+#     Based on index = 1 of @players_age and 
+#     index = 0 of @players_name.
+# 
+#     20, "Alex",  "Stewart"
+#     20, "Alex",  "Jones"
+#     18, "Alex",  "Stewart"
+#     18, "Alex",  "Jones"
+#     28, "Joe",   "Root"
+#     28, "Joe",   "Blog"
+#     38, "Mike",  "Gatting"
+#     18, "Simon", "Duane"
+
+player_ages = [
+    [20, "Alex"  ],
+    [28, "Joe"   ],
+    [38, "Mike"  ],
+    [18, "Alex"  ],
+    [25, "David" ],
+    [18, "Simon" ],
+]
+player_ages_key = 1
+
+player_names = [
+    ["Alex", "Stewart"],
+    ["Joe",  "Root"   ],
+    ["Mike", "Gatting"],
+    ["Joe",  "Blog"   ],
+    ["Alex", "Jones"  ],
+    ["Simon","Duane"  ],
+]
+player_names_key = 0
+
+def format_col(s):
+    if type(s) == int:
+        return str(s)
+    else:
+        return '"'+s+'"'
+
+def hash_join(table1, key1, table2, key2):
+    build = {}
+    for row in table1:
+        key = row[key1]
+        if key not in build:
+            build[key] = []
+        build[key].append(row)
+    result = []
+    for row_probe in table2:
+        key = row_probe[key2]
+        for row_build in build[key]:
+            row = row_build + \
+                  row_probe[:key2] + \
+                  row_probe[key2+1:]
+            row = [format_col(x) for x in row]
+            result.append(row)
+    return result
+
+result = hash_join(player_ages, player_ages_key,
+				   player_names, player_names_key)
+for row in result:
+    print(', '.join(row))