From 0f82cedf5540373ca39a87f436d47c846ab0bcb5 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Thu, 26 May 2016 23:28:07 +0200
Subject: [PATCH] BUG: preserve metadata on merge/concat (#247, #320) (#322)

---
 geopandas/geodataframe.py     | 22 +++++++++----
 geopandas/tests/test_merge.py | 62 +++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 7 deletions(-)
 create mode 100644 geopandas/tests/test_merge.py

diff --git a/geopandas/geodataframe.py b/geopandas/geodataframe.py
index ef6e071..12e24b9 100644
--- a/geopandas/geodataframe.py
+++ b/geopandas/geodataframe.py
@@ -409,10 +409,18 @@ class GeoDataFrame(GeoPandasBase, DataFrame):
         return GeoDataFrame
 
     def __finalize__(self, other, method=None, **kwargs):
-        """ propagate metadata from other to self """
-        # NOTE: backported from pandas master (upcoming v0.13)
-        for name in self._metadata:
-            object.__setattr__(self, name, getattr(other, name, None))
+        """propagate metadata from other to self """
+        # merge operation: using metadata of the left object
+        if method == 'merge':
+            for name in self._metadata:
+                object.__setattr__(self, name, getattr(other.left, name, None))
+        # concat operation: using metadata of the first object
+        elif method == 'concat':
+            for name in self._metadata:
+                object.__setattr__(self, name, getattr(other.objs[0], name, None))
+        else:
+            for name in self._metadata:
+                object.__setattr__(self, name, getattr(other, name, None))
         return self
 
     def copy(self, deep=True):
@@ -443,7 +451,7 @@ class GeoDataFrame(GeoPandasBase, DataFrame):
 
     def dissolve(self, by=None, aggfunc='first'):
         """
-        Dissolve geometries within `groupby` into single observation. 
+        Dissolve geometries within `groupby` into single observation.
 
         Parameters
         ----------
@@ -473,14 +481,14 @@ class GeoDataFrame(GeoPandasBase, DataFrame):
             merged_geom = block.unary_union
 
             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), 
+            merged_w_index = GeoSeries(merged_geom, index=Index(Series(new_index),name=by),
                                           name=self.geometry.name)
             return merged_w_index
 
 
         g = geometry.groupby(by=by, group_keys=False).apply(merge_geometries)
 
-        aggregated_geometry = GeoDataFrame(g, 
+        aggregated_geometry = GeoDataFrame(g,
                                            index=g.index,
                                            geometry=self.geometry.name)
         # Recombine
diff --git a/geopandas/tests/test_merge.py b/geopandas/tests/test_merge.py
new file mode 100644
index 0000000..17cd238
--- /dev/null
+++ b/geopandas/tests/test_merge.py
@@ -0,0 +1,62 @@
+from __future__ import absolute_import
+
+import pandas as pd
+from shapely.geometry import Point
+
+from geopandas import GeoDataFrame, GeoSeries
+from geopandas.tests.util import unittest
+
+
+class TestMerging(unittest.TestCase):
+
+    def setUp(self):
+
+        self.gseries = GeoSeries([Point(i, i) for i in range(3)])
+        self.series = pd.Series([1, 2, 3])
+        self.gdf = GeoDataFrame({'geometry': self.gseries, 'values': range(3)})
+        self.df = pd.DataFrame({'col1': [1, 2, 3], 'col2': [0.1, 0.2, 0.3]})
+
+    def _check_metadata(self, gdf, geometry_column_name='geometry', crs=None):
+
+        self.assertEqual(gdf._geometry_column_name, geometry_column_name)
+        self.assertEqual(gdf.crs, crs)
+
+    def test_merge(self):
+
+        res = self.gdf.merge(self.df, left_on='values', right_on='col1')
+
+        # check result is a GeoDataFrame
+        self.assert_(isinstance(res, GeoDataFrame))
+
+        # check geometry property gives GeoSeries
+        self.assert_(isinstance(res.geometry, GeoSeries))
+
+        # check metadata
+        self._check_metadata(res)
+
+        ## test that crs and other geometry name are preserved
+        self.gdf.crs = {'init' :'epsg:4326'}
+        self.gdf = (self.gdf.rename(columns={'geometry': 'points'})
+                            .set_geometry('points'))
+        res = self.gdf.merge(self.df, left_on='values', right_on='col1')
+        self.assert_(isinstance(res, GeoDataFrame))
+        self.assert_(isinstance(res.geometry, GeoSeries))
+        self._check_metadata(res, 'points', self.gdf.crs)
+
+    def test_concat_axis0(self):
+
+        res = pd.concat([self.gdf, self.gdf])
+
+        self.assertEqual(res.shape, (6, 2))
+        self.assert_(isinstance(res, GeoDataFrame))
+        self.assert_(isinstance(res.geometry, GeoSeries))
+        self._check_metadata(res)
+
+    def test_concat_axis1(self):
+
+        res = pd.concat([self.gdf, self.df], axis=1)
+
+        self.assertEqual(res.shape, (3, 4))
+        self.assert_(isinstance(res, GeoDataFrame))
+        self.assert_(isinstance(res.geometry, GeoSeries))
+        self._check_metadata(res)