dissolve bug fixes (#323)

geopandas/geodataframe.py

@@ -449,9 +449,14 @@ def plot(self, *args, **kwargs):
     plot.__doc__ = plot_dataframe.__doc__
 
 
-    def dissolve(self, by=None, aggfunc='first'):
+    def dissolve(self, by=None, aggfunc='first', as_index=True):
         """
         Dissolve geometries within `groupby` into single observation.
+        This is accomplished by applying the `unary_union` method
+        to all geometries within a groupself.
+
+        Observations associated with each `groupby` group will be aggregated
+        using the `aggfunc`.
 
         Parameters
         ----------
@@ -460,40 +465,35 @@ def dissolve(self, by=None, aggfunc='first'):
         aggfunc : function or string, default "first"
             Aggregation function for manipulation of data associated
             with each group. Passed to pandas `groupby.agg` method.
+        as_index : boolean, default True
+            If true, groupby columns become index of result.
 
         Returns
         -------
         GeoDataFrame
         """
 
         # Process non-spatial component
-        data = self.drop(labels=self.geometry.name, axis=1).copy()
+        data = self.drop(labels=self.geometry.name, axis=1)
         aggregated_data = data.groupby(by=by).agg(aggfunc)
 
 
         # Process spatial component
-        groupby_plus_geometry_cols = [self.geometry.name]
-        groupby_plus_geometry_cols.append(by)
-        geometry = self[groupby_plus_geometry_cols].copy()
-
         def merge_geometries(block):
-
             merged_geom = block.unary_union
+            return merged_geom
 
-            new_index = block.drop(self.geometry.name, axis=1).iloc[0][by]
-            merged_w_index = GeoSeries(merged_geom, index=Index(Series(new_index),name=by),
-                                          name=self.geometry.name)
-            return merged_w_index
-
+        g = self.groupby(by=by, group_keys=False)[self.geometry.name].agg(merge_geometries)
 
-        g = geometry.groupby(by=by, group_keys=False).apply(merge_geometries)
-
-        aggregated_geometry = GeoDataFrame(g,
-                                           index=g.index,
-                                           geometry=self.geometry.name)
+        # Aggregate
+        aggregated_geometry = GeoDataFrame(g, geometry=self.geometry.name)
         # Recombine
         aggregated = aggregated_geometry.join(aggregated_data)
-        aggregated = aggregated.set_geometry(self.geometry.name)
+
+        # Reset if requested
+        if not as_index:
+            aggregated = aggregated.reset_index()
+
         return aggregated
 
 def _dataframe_set_geometry(self, col, drop=False, inplace=False, crs=None):

tests/test_dissolve.py → geopandas/tests/test_dissolve.py

@@ -8,6 +8,11 @@
 from .util import unittest, download_nybb
 from pandas.util.testing import assert_frame_equal
 from pandas import Index
+from distutils.version import LooseVersion
+import pandas as pd
+
+pandas_0_15_problem = 'fails under pandas < 0.16 due to issue 324,'\
+                      'not problem with dissolve.'
 
 class TestDataFrame(unittest.TestCase):
 
@@ -28,7 +33,7 @@ def setUp(self):
         others = self.polydf.loc[0:2,]
 
         collapsed = [others.geometry.unary_union, manhattan_bronx.geometry.unary_union]
-        merged_shapes = GeoDataFrame({'myshapes': collapsed}, geometry='myshapes', 
+        merged_shapes = GeoDataFrame({'myshapes': collapsed}, geometry='myshapes',
                              index=Index([5,6], name='manhattan_bronx'))
 
         # Different expected results
@@ -40,25 +45,39 @@ def setUp(self):
         self.mean['BoroCode'] = [4,1.5]
 
 
+    @unittest.skipIf(str(pd.__version__) < LooseVersion('0.16'), pandas_0_15_problem)
     def test_geom_dissolve(self):
         test = self.polydf.dissolve('manhattan_bronx')
         self.assertTrue(test.geometry.name == 'myshapes')
         self.assertTrue(test.geom_almost_equals(self.first).all())
 
+    @unittest.skipIf(str(pd.__version__) < LooseVersion('0.16'), pandas_0_15_problem)
     def test_first_dissolve(self):
         test = self.polydf.dissolve('manhattan_bronx')
-        test = test.drop('myshapes', axis=1)
-        first = self.first.drop('myshapes', axis=1)
-        assert_frame_equal(first, test)
+        assert_frame_equal(self.first, test, check_column_type=False)
 
+    @unittest.skipIf(str(pd.__version__) < LooseVersion('0.16'), pandas_0_15_problem)
     def test_mean_dissolve(self):
         test = self.polydf.dissolve('manhattan_bronx', aggfunc='mean')
-        test = test.drop('myshapes', axis=1)
-        mean = self.mean.drop('myshapes', axis=1)
-        assert_frame_equal(mean, test)
+        assert_frame_equal(self.mean, test, check_column_type=False)
 
         test = self.polydf.dissolve('manhattan_bronx', aggfunc=np.mean)
-        test = test.drop('myshapes', axis=1)
-        assert_frame_equal(mean, test)
+        assert_frame_equal(self.mean, test, check_column_type=False)
+
+    @unittest.skipIf(str(pd.__version__) < LooseVersion('0.16'), pandas_0_15_problem)
+    def test_multicolumn_dissolve(self):
+        multi = self.polydf.copy()
+        multi['dup_col'] = multi.manhattan_bronx
+        multi_test = multi.dissolve(['manhattan_bronx', 'dup_col'], aggfunc='first')
+
+        first = self.first.copy()
+        first['dup_col'] = first.index
+        first = first.set_index([first.index, 'dup_col'])
 
+        assert_frame_equal(multi_test, first, check_column_type=False)
 
+    @unittest.skipIf(str(pd.__version__) < LooseVersion('0.16'), pandas_0_15_problem)
+    def test_reset_index(self):
+        test = self.polydf.dissolve('manhattan_bronx', as_index=False)
+        comparison = self.first.reset_index()
+        assert_frame_equal(comparison, test, check_column_type=False)