Implement competition ranking. Closes #125.

CHANGELOG

@@ -1,7 +1,7 @@
 0.8.0
 -----
 
-
+* Competition ranking implemented as default. (#125)
 
 0.7.0
 -----

agate/columns/base.py

@@ -10,7 +10,7 @@
 import six
 
 from agate.exceptions import ColumnDoesNotExistError
-from agate.utils import memoize
+from agate.utils import NullOrder, memoize
 
 class ColumnMapping(Mapping):
     """
@@ -119,12 +119,21 @@ def get_data_without_nulls(self):
         """
         return tuple(d for d in self.get_data() if d is not None)
 
+    def _null_handler(self, k):
+        """
+        Key method for sorting nulls correctly.
+        """
+        if k is None:
+            return NullOrder()
+
+        return k
+
     @memoize
     def get_data_sorted(self):
         """
         Get the data contained in this column sorted.
         """
-        return sorted(self.get_data())
+        return sorted(self.get_data(), key=self._null_handler)
 
     @memoize
     def has_nulls(self):

agate/computations.py

@@ -156,27 +156,31 @@ class Rank(Computation):
     """
     Computes rank order of the values in a column.
 
-    NOTE: This rank algorithm is overly-simplistic and currently does not
-    handle ties.
+    Uses the "competition" ranking method: if there are four values and the
+    middle two are tied, then the output will be :code:`[1, 2, 2, 4]`.
+
+    Null values will always be ranked last.
     """
     def __init__(self, column_name):
         self._column_name = column_name
 
     def get_computed_column_type(self, table):
         return NumberType()
 
-    def _null_handler(self, k):
-        if k is None:
-            return NullOrder()
+    def prepare(self, table):
+        self._ranks = {}
+        rank = 0
+
+        for c in table.columns[self._column_name].get_data_sorted():
+            rank += 1
 
-        return k
+            if c in self._ranks:
+                continue
 
-    def prepare(self, table):
-        values = [row[self._column_name] for row in table.rows]
-        self._rank_column = sorted(values, key=self._null_handler)
+            self._ranks[c] = rank
 
     def run(self, row):
-        return self._rank_column.index(row[self._column_name]) + 1
+         return self._ranks[row[self._column_name]]
 
 class PercentileRank(Rank):
     """

tests/test_computations.py

@@ -104,12 +104,6 @@ def test_rank_number(self):
 
         self.assertEqual(len(new_table.rows), 4)
         self.assertEqual(len(new_table.columns), 5)
-
-        self.assertSequenceEqual(new_table.rows[0], ('a', 2, 3, 4, 1))
-        self.assertSequenceEqual(new_table.rows[1], (None, 3, 5, None, 3))
-        self.assertSequenceEqual(new_table.rows[2], ('a', 2, 4, None, 1))
-        self.assertSequenceEqual(new_table.rows[3], ('b', 3, 4, None, 3))
-
         self.assertSequenceEqual(new_table.columns['rank'], (1, 3, 1, 3))
 
     def test_rank_text(self):
@@ -119,29 +113,8 @@ def test_rank_text(self):
 
         self.assertEqual(len(new_table.rows), 4)
         self.assertEqual(len(new_table.columns), 5)
-
-        self.assertSequenceEqual(new_table.rows[0], ('a', 2, 3, 4, 1))
-        self.assertSequenceEqual(new_table.rows[1], (None, 3, 5, None, 4))
-        self.assertSequenceEqual(new_table.rows[2], ('a', 2, 4, None, 1))
-        self.assertSequenceEqual(new_table.rows[3], ('b', 3, 4, None, 3))
-
         self.assertSequenceEqual(new_table.columns['rank'], (1, 4, 1, 3))
 
-    def test_rank_column_name(self):
-        new_table = self.table.compute([
-            ('rank', Rank('two'))
-        ])
-
-        self.assertEqual(len(new_table.rows), 4)
-        self.assertEqual(len(new_table.columns), 5)
-
-        self.assertSequenceEqual(new_table.rows[0], ('a', 2, 3, 4, 1))
-        self.assertSequenceEqual(new_table.rows[1], (None, 3, 5, None, 3))
-        self.assertSequenceEqual(new_table.rows[2], ('a', 2, 4, None, 1))
-        self.assertSequenceEqual(new_table.rows[3], ('b', 3, 4, None, 3))
-
-        self.assertSequenceEqual(new_table.columns['rank'], (1, 3, 1, 3))
-
     def test_percentile_rank(self):
         rows = [(n,) for n in range(1, 1001)]