Compute Non-standard Statistics

Allow computation of statistics not directly implemented by the program
or the np.ma package.

Added two options:
add_stats = [‘stat1’, ‘stat2’]   # List of statistics to be computed
add_func=‘myfunc’    # Module where the functions that compute these
statistics are defined

src/rasterstats/main.py

@@ -34,7 +34,8 @@ def raster_stats(*args, **kwargs):
 
 def zonal_stats(vectors, raster, layer_num=0, band_num=1, nodata_value=None, 
                  global_src_extent=False, categorical=False, stats=None, 
-                 copy_properties=False, all_touched=False, transform=None):
+                 copy_properties=False, all_touched=False, transform=None,
+                 add_stats=[None], add_func=[None]):
     """Summary statistics of a raster, broken out by vector geometries.
 
     Attributes
@@ -78,6 +79,9 @@ def zonal_stats(vectors, raster, layer_num=0, band_num=1, nodata_value=None,
     transform : list of float, optional
         GDAL-style geotransform coordinates when `raster` is an ndarray.
         Required when `raster` is an ndarray, otherwise ignored.
+    add_stats : List with name additional statistics to compute, optional
+        Each name in add_stats is a string with the name of a function 
+        that takes Numpy (masked) matrices and computes and returns a statistic 
 
     Returns
     -------
@@ -296,6 +300,19 @@ def zonal_stats(vectors, raster, layer_num=0, band_num=1, nodata_value=None,
                 except KeyError:
                     rmax = float(masked.max())
                 feature_stats['range'] = rmax - rmin
+            if add_stats:
+                if add_func:
+                    try:
+                        exec('from '+add_func+' import *')
+                    except:
+                        print('Could not load module %s') % add_func
+                        break
+                    for mystat in range(len(add_stats)):
+                        adstat=add_stats[mystat]
+                        try:
+                            exec('feature_stats["'+adstat+'"] = '+adstat+'(masked)')
+                        except:
+                            print('Statistic %s in add_stats not defined in add_func') % adstat
 
         # Use the enumerated id as __fid__
         feature_stats['__fid__'] = i

tests/myfunc.py

@@ -0,0 +1,7 @@
+#!/usr/bin/env python
+# Additional functions to be used in raster stat computation
+from __future__ import division
+import numpy as np
+
+def mymean(x):
+    return np.ma.mean(x)

tests/test_zonal.py

@@ -8,6 +8,9 @@
                               OGRError, feature_to_geojson, bbox_to_pixel_offsets
 from shapely.geometry import shape, box
 import json
+import sys
+
+sys.path.append(os.path.dirname(os.path.abspath(__file__)))
 
 DATA = os.path.join(os.path.dirname(os.path.abspath(__file__)), "data")
 raster = os.path.join(DATA, 'slope.tif')
@@ -389,3 +392,12 @@ def test_featurecollection():
     # geointerface featurecollection
     stats2 = zonal_stats(df, raster)
     assert stats == stats2
+
+def test_add_stats():
+    from geopandas import GeoDataFrame
+    polygons = os.path.join(DATA, 'polygons.shp')
+    df = GeoDataFrame.from_file(polygons)
+    mymean= lambda x: np.ma.mean(x)
+    stats = zonal_stats(df.geometry, raster, add_stats=['mymean'], add_func='myfunc')
+    for i in range(len(stats)):
+        assert stats[i]['mean'] == stats[i]['mymean']