BUG: retain index names of input frames to sjoin (geopandas#545)

* BUG: sjoin modifies original frame (geopandas#525)

Original pandas table's index names are no
longer changed by sjoin() call. Includes
some unit-tests. Fixes issue geopandas#525

* New code to fix issue that is compatible with pandas 0.16.2 - 0.20.3

* applied suggested changes to test_sjoin.py

geopandas/tools/sjoin.py

@@ -56,9 +56,11 @@ def sjoin(left_df, right_df, how='inner', op='intersects',
     # index in geopandas may be any arbitrary dtype. so reset both indices now
     # and store references to the original indices, to be reaffixed later.
     # GH 352
-    left_df.index.name = index_left
-    right_df.index.name = index_right
+    left_df = left_df.copy(deep=True)
+    left_df.index = left_df.index.rename(index_left)
     left_df = left_df.reset_index()
+    right_df = right_df.copy(deep=True)
+    right_df.index = right_df.index.rename(index_right)
     right_df = right_df.reset_index()
 
     if op == "within":

geopandas/tools/tests/test_sjoin.py

@@ -83,7 +83,7 @@ def test_inner(self, op, dfs):
         index, df1, df2, expected = dfs
 
         res = sjoin(df1, df2, how='inner', op=op)
-
+        
         exp = expected[op].dropna().copy()
         exp = exp.drop('geometry_y', axis=1).rename(
             columns={'geometry_x': 'geometry'})
@@ -208,6 +208,15 @@ def test_sjoin_duplicate_column_name(self):
         assert 'Shape_Area_left' in df.columns
         assert 'Shape_Area_right' in df.columns
 
+    @pytest.mark.parametrize('how', ['left', 'right', 'inner'])
+    def test_sjoin_named_index(self,how):
+        #original index names should be unchanged
+        pointdf2 = self.pointdf.copy()
+        pointdf2.index.name = 'pointid'
+        df = sjoin(pointdf2, self.polydf, how=how)
+        assert pointdf2.index.name == 'pointid'
+        assert self.polydf.index.name == None
+
     def test_sjoin_values(self):
         # GH190
         self.polydf.index = [1, 3, 4, 5, 6]