Implement DataField.dist method

Fix #225

Signed-off-by: Byron Ruth <b@devel.io>

avocado/models.py

@@ -4,6 +4,7 @@
 from warnings import warn
 from datetime import datetime
 from django.db import models
+from django.db.models import Count
 from django.contrib.sites.models import Site
 from django.contrib.auth.models import User, Group
 from django.utils.encoding import smart_unicode
@@ -576,7 +577,7 @@ def coded_values(self, queryset=None):
     # Data Aggregation Properties
     def groupby(self, *args, **kwargs):
         return Aggregator(
-            self.field, queryset=kwargs.get('queryset', None)).groupby(*args)
+            self.field, queryset=kwargs.get('queryset')).groupby(*args)
 
     @cached_method(version='data_version')
     def count(self, *args, **kwargs):
@@ -589,43 +590,43 @@ def count(self, *args, **kwargs):
     def max(self, *args, **kwargs):
         "Returns the maximum value."
         return Aggregator(
-            self.field, queryset=kwargs.get('queryset', None)).max(*args)
+            self.field, queryset=kwargs.get('queryset')).max(*args)
 
     @cached_method(version='data_version')
     def min(self, *args, **kwargs):
         "Returns the minimum value."
         return Aggregator(
-            self.field, queryset=kwargs.get('queryset', None)).min(*args)
+            self.field, queryset=kwargs.get('queryset')).min(*args)
 
     @cached_method(version='data_version')
     def avg(self, *args, **kwargs):
         "Returns the average value. Only applies to quantitative data."
         if self.simple_type == 'number':
             return Aggregator(
-                self.field, queryset=kwargs.get('queryset', None)).avg(*args)
+                self.field, queryset=kwargs.get('queryset')).avg(*args)
 
     @cached_method(version='data_version')
     def sum(self, *args, **kwargs):
         "Returns the sum of values. Only applies to quantitative data."
         if self.simple_type == 'number':
             return Aggregator(
-                self.field, queryset=kwargs.get('queryset', None)).sum(*args)
+                self.field, queryset=kwargs.get('queryset')).sum(*args)
 
     @cached_method(version='data_version')
     def stddev(self, *args, **kwargs):
         "Returns the standard deviation. Only applies to quantitative data."
         if self.simple_type == 'number':
             return Aggregator(
                 self.field,
-                queryset=kwargs.get('queryset', None)).stddev(*args)
+                queryset=kwargs.get('queryset')).stddev(*args)
 
     @cached_method(version='data_version')
     def variance(self, *args, **kwargs):
         "Returns the variance. Only applies to quantitative data."
         if self.simple_type == 'number':
             return Aggregator(
                 self.field,
-                queryset=kwargs.get('queryset', None)).variance(*args)
+                queryset=kwargs.get('queryset')).variance(*args)
 
     @cached_method(version='data_version')
     def sparsity(self, *args, **kwargs):
@@ -646,6 +647,17 @@ def sparsity(self, *args, **kwargs):
 
         return nulls / float(count)
 
+    @cached_method(version='data_version')
+    def dist(self, queryset=None):
+        if queryset is None:
+            queryset = self.model.objects.all()
+
+        queryset = queryset.annotate(cnt=Count(self.value_field_name))\
+            .values_list(self.value_field_name, 'cnt')\
+            .order_by(self.value_field_name)
+
+        return tuple(queryset)
+
     # Translator Convenience Methods
     @property
     def operators(self):

tests/cases/models/tests.py

@@ -325,6 +325,22 @@ def test_random(self):
         self.assertRaises(ValueError, self.budget.random, 2, queryset=queryset)
         self.assertEqual(len(self.budget.random(1)), 1)
 
+    def test_dist(self):
+        self.assertEqual(self.first_name.dist(), (
+                        ('Aaron', 1),
+                        ('Eric', 1),
+                        ('Erick', 1),
+                        ('Erin', 1),
+                        ('Mel', 1),
+                        ('Zac', 1)))
+
+        queryset = self.first_name.model.objects\
+            .filter(first_name__startswith='E')
+        self.assertEqual(self.first_name.dist(queryset=queryset), (
+                        ('Eric', 1),
+                        ('Erick', 1),
+                        ('Erin', 1)))
+
 
 class DataConceptTestCase(TestCase):
     def setUp(self):