Support by reductions in datashader operations

holoviews/operation/datashader.py

@@ -252,7 +252,7 @@ def _get_aggregator(self, element, add_field=True):
             agg = self._agg_methods[agg]()
 
         elements = element.traverse(lambda x: x, [Element])
-        if add_field and agg.column is None and not isinstance(agg, (rd.count, rd.any)):
+        if add_field and getattr(agg, 'column', False) is None and not isinstance(agg, (rd.count, rd.any)):
             if not elements:
                 raise ValueError('Could not find any elements to apply '
                                  '%s operation to.' % type(self).__name__)
@@ -291,6 +291,10 @@ def _get_agg_params(self, element, x, y, agg_fn, bounds):
         params = dict(get_param_values(element), kdims=[x, y],
                       datatype=['xarray'], bounds=bounds)
 
+        category = None
+        if hasattr(agg_fn, 'reduction'):
+            category = agg_fn.cat_column
+            agg_fn = agg_fn.reduction
         column = agg_fn.column if agg_fn else None
         if column:
             dims = [d for d in element.dimensions('ranges') if d == column]
@@ -300,6 +304,8 @@ def _get_agg_params(self, element, x, y, agg_fn, bounds):
                                  "dimension." % (column,element))
             name = '%s Count' % column if isinstance(agg_fn, ds.count_cat) else column
             vdims = [dims[0].clone(name)]
+        elif category:
+            vdims = Dimension('%s Count' % category)
         else:
             vdims = Dimension('Count')
         params['vdims'] = vdims
@@ -332,7 +338,6 @@ class aggregate(AggregationOperation):
     the linked plot.
     """
 
-
     @classmethod
     def get_agg_data(cls, obj, category=None):
         """
@@ -409,7 +414,10 @@ def get_agg_data(cls, obj, category=None):
 
     def _process(self, element, key=None):
         agg_fn = self._get_aggregator(element)
-        category = agg_fn.column if isinstance(agg_fn, ds.count_cat) else None
+        if hasattr(agg_fn, 'cat_column'):
+            category = agg_fn.cat_column
+        else:
+            category = agg_fn.column if isinstance(agg_fn, ds.count_cat) else None
 
         if overlay_aggregate.applies(element, agg_fn):
             params = dict(

holoviews/operation/element.py

@@ -640,7 +640,7 @@ class histogram(Operation):
     bin_range = param.NumericTuple(default=None, length=2,  doc="""
       Specifies the range within which to compute the bins.""")
 
-    bins = param.ClassSelector(default=None, class_=(np.ndarray, list, tuple), doc="""
+    bins = param.ClassSelector(default=None, class_=(np.ndarray, list, tuple, str), doc="""
       An explicit set of bin edges.""")
 
     cumulative = param.Boolean(default=False, doc="""

holoviews/tests/operation/testdatashader.py

@@ -3,10 +3,12 @@
 from unittest import SkipTest, skipIf
 
 import numpy as np
+
 from holoviews import (Dimension, Curve, Points, Image, Dataset, RGB, Path,
                        Graph, TriMesh, QuadMesh, NdOverlay, Contours, Spikes,
                        Spread, Area, Segments, Polygons)
 from holoviews.element.comparison import ComparisonTestCase
+from numpy import nan
 
 try:
     import datashader as ds
@@ -35,6 +37,8 @@
 cudf_skip = skipIf(cudf is None, "cuDF not available")
 
 
+
+
 class DatashaderAggregateTests(ComparisonTestCase):
     """
     Tests for datashader aggregation
@@ -620,6 +624,36 @@ def test_multi_poly_rasterize(self):
 
 
 
+class DatashaderCatAggregateTests(ComparisonTestCase):
+
+    def setUp(self):
+        if ds_version < '0.11.0':
+            raise SkipTest('Regridding operations require datashader>=0.11.0')
+
+    def test_aggregate_points_categorical(self):
+        points = Points([(0.2, 0.3, 'A'), (0.4, 0.7, 'B'), (0, 0.99, 'C')], vdims='z')
+        img = aggregate(points, dynamic=False,  x_range=(0, 1), y_range=(0, 1),
+                        width=2, height=2, aggregator=ds.by('z', ds.count()))
+        xs, ys = [0.25, 0.75], [0.25, 0.75]
+        expected = NdOverlay({'A': Image((xs, ys, [[1, 0], [0, 0]]), vdims='z Count'),
+                              'B': Image((xs, ys, [[0, 0], [1, 0]]), vdims='z Count'),
+                              'C': Image((xs, ys, [[0, 0], [1, 0]]), vdims='z Count')},
+                             kdims=['z'])
+        self.assertEqual(img, expected)
+
+
+    def test_aggregate_points_categorical_mean(self):
+        points = Points([(0.2, 0.3, 'A', 0.1), (0.4, 0.7, 'B', 0.2), (0, 0.99, 'C', 0.3)], vdims=['cat', 'z'])
+        img = aggregate(points, dynamic=False,  x_range=(0, 1), y_range=(0, 1),
+                        width=2, height=2, aggregator=ds.by('cat', ds.mean('z')))
+        xs, ys = [0.25, 0.75], [0.25, 0.75]
+        expected = NdOverlay({'A': Image((xs, ys, [[0.1, nan], [nan, nan]]), vdims='z'),
+                              'B': Image((xs, ys, [[nan, nan], [0.2, nan]]), vdims='z'),
+                              'C': Image((xs, ys, [[nan, nan], [0.3, nan]]), vdims='z')},
+                             kdims=['cat'])
+        self.assertEqual(img, expected)
+
+
 
 class DatashaderShadeTests(ComparisonTestCase):
 
@@ -633,9 +667,9 @@ def test_shade_categorical_images_xarray(self):
                                      datatype=['xarray'], vdims='z Count')},
                          kdims=['z'])
         shaded = shade(data)
-        r = [[228, 255], [66, 255]]
-        g = [[26, 255], [150, 255]]
-        b = [[28, 255], [129, 255]]
+        r = [[228, 120], [66, 120]]
+        g = [[26, 109], [150, 109]]
+        b = [[28, 95], [129, 95]]
         a = [[40, 0], [255, 0]]
         expected = RGB((xs, ys, r, g, b, a), datatype=['grid'],
                        vdims=RGB.vdims+[Dimension('A', range=(0, 1))])
@@ -651,9 +685,9 @@ def test_shade_categorical_images_grid(self):
                                      datatype=['grid'], vdims='z Count')},
                          kdims=['z'])
         shaded = shade(data)
-        r = [[228, 255], [66, 255]]
-        g = [[26, 255], [150, 255]]
-        b = [[28, 255], [129, 255]]
+        r = [[228, 120], [66, 120]]
+        g = [[26, 109], [150, 109]]
+        b = [[28, 95], [129, 95]]
         a = [[40, 0], [255, 0]]
         expected = RGB((xs, ys, r, g, b, a), datatype=['grid'],
                        vdims=RGB.vdims+[Dimension('A', range=(0, 1))])