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I have a GeoPandas GeoDataFrame with a geometry column that contains both POLYGONs and MULTIPOLYGONs. How do I filter only MULTIPOLYGONs?

I used this approach, but I am sure there might be better ones:

# 'at' because it's data about Austria
at_geometries.loc[at_geometries["geometry"].astype("str").str.startswith("MULTI")]
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  • Is that slow or what is the problem?
    – BERA
    Oct 13, 2021 at 8:26
  • It's a bit slow (because it has to parse as strings the whole list of points in the geometry) but I could not find any other way. I guess there is no "official"/built-in way of doing this, right?
    – baggiponte
    Oct 13, 2021 at 8:37

2 Answers 2

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11

There are many solutions (see How to filter a geodataframe by geometry type? for example)

With .loc as you but with geometry.type or geom_type

gdf0 = gdf.loc[gdf.geometry.geometry.type=='MultiPolygon']
gdf0
    ID                 geometry
0    1  MULTIPOLYGON (((244697.452 1000369.231, 244827...
1    5  MULTIPOLYGON (((244912.829 1000603.336, 245042...
2    8  MULTIPOLYGON (((244732.568 1000040.313, 244862...

gdf0= gdf.loc[gdf.geometry.geom_type=='MultiPolygon']
idem

With apply,lambda and type

gdf1 = gdf[gdf.geometry.apply(lambda x : x.type=='MultiPolygon')]
gdf1
    ID                 geometry
0    1  MULTIPOLYGON (((244697.452 1000369.231, 244827...
1    5  MULTIPOLYGON (((244912.829 1000603.336, 245042...
2    8  MULTIPOLYGON (((244732.568 1000040.313, 244862...

With geom_type

gdf2 = gdf[gdf.geom_type=='MultiPolygon']
gdf2
    ID                 geometry
0    1  MULTIPOLYGON (((244697.452 1000369.231, 244827...
1    5  MULTIPOLYGON (((244912.829 1000603.336, 245042...
2    8  MULTIPOLYGON (((244732.568 1000040.313, 244862...

With geometry.type as Kadir Şahbaz

gdf3 = gdf[gdf.geometry.type=="MultiPolygon"]
gdf3
    ID                 geometry
0    1  MULTIPOLYGON (((244697.452 1000369.231, 244827...
1    5  MULTIPOLYGON (((244912.829 1000603.336, 245042...
2    8  MULTIPOLYGON (((244732.568 1000040.313, 244862...
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  • As usually @gene aggregates all the possible approaches. Thank you :)
    – Taras
    Oct 13, 2021 at 10:42
  • Thank you, this is really great! I did not know geopandas had this great attribute(s). And thank you for the thorough reply!
    – baggiponte
    Oct 14, 2021 at 8:05
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Using geometry.type=="MULTIPOLYGON" is (15 times in my computer) faster.

at_geometries[at_geometries.geometry.type=="MULTIPOLYGON"]`
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