Add dim-expression support in Dataset.select

holoviews/core/data/__init__.py

@@ -335,7 +335,7 @@ def add_dimension(self, dimension, dim_pos, dim_val, vdim=False, **kwargs):
         return self.clone(data, **dimensions)
 
 
-    def select(self, selection_specs=None, **selection):
+    def select(self, selection_expr=None, selection_specs=None, **selection):
         """Applies selection by dimension name
 
         Applies a selection along the dimensions of the object using
@@ -360,7 +360,14 @@ def select(self, selection_specs=None, **selection):
 
             ds.select(x=[0, 1, 2])
 
+        * predicate expression: A holoviews.dim expression, e.g.:
+
+            from holoviews import dim
+            ds.select(selection_expr=dim('x') % 2 == 0)
+
         Args:
+            selection_expr: holoviews.dim predicate expression
+                specifying selection.
             selection_specs: List of specs to match on
                 A list of types, functions, or type[.group][.label]
                 strings specifying which objects to apply the
@@ -373,15 +380,33 @@ def select(self, selection_specs=None, **selection):
             Returns an Dimensioned object containing the selected data
             or a scalar if a single value was selected
         """
+        from ...util.transform import dim
+        if selection_expr is not None and not isinstance(selection_expr, dim):
+            raise ValueError("""\
+The first positional argument to the Dataset.select method is expected to be a
+holoviews.util.transform.dim expression. Use the selection_specs keyword
+argument to specify a selection specification""")
+
         if selection_specs is not None and not isinstance(selection_specs, (list, tuple)):
             selection_specs = [selection_specs]
-        selection = {dim: sel for dim, sel in selection.items()
-                     if dim in self.dimensions()+['selection_mask']}
+        selection = {dim_name: sel for dim_name, sel in selection.items()
+                     if dim_name in self.dimensions()+['selection_mask']}
         if (selection_specs and not any(self.matches(sp) for sp in selection_specs)
-            or not selection):
+                or (not selection and not selection_expr)):
             return self
 
-        data = self.interface.select(self, **selection)
+        # Handle selection dim expression
+        if selection_expr is not None:
+            mask = selection_expr.apply(self, compute=False, keep_index=True)
+            dataset = self[mask]
+        else:
+            dataset = self
+
+        # Handle selection kwargs
+        if selection:
+            data = dataset.interface.select(dataset, **selection)
+        else:
+            data = dataset.data
 
         if np.isscalar(data):
             return data
@@ -453,7 +478,7 @@ def __getitem__(self, slices):
                object.
         """
         slices = util.process_ellipses(self, slices, vdim_selection=True)
-        if isinstance(slices, np.ndarray) and slices.dtype.kind == 'b':
+        if getattr(getattr(slices, 'dtype', None), 'kind', None) == 'b':
             if not len(slices) == len(self):
                 raise IndexError("Boolean index must match length of sliced object")
             return self.clone(self.select(selection_mask=slices))

holoviews/core/data/array.py

@@ -123,7 +123,9 @@ def sort(cls, dataset, by=[], reverse=False):
 
 
     @classmethod
-    def values(cls, dataset, dim, expanded=True, flat=True, compute=True):
+    def values(
+            cls, dataset, dim, expanded=True, flat=True, compute=True, keep_index=False
+    ):
         data = dataset.data
         dim_idx = dataset.get_dimension_index(dim)
         if data.ndim == 1:

holoviews/core/data/dask.py

@@ -90,12 +90,23 @@ def sort(cls, dataset, by=[], reverse=False):
         return dataset.data
 
     @classmethod
-    def values(cls, dataset, dim, expanded=True, flat=True, compute=True):
+    def values(
+            cls,
+            dataset,
+            dim,
+            expanded=True,
+            flat=True,
+            compute=True,
+            keep_index=False,
+    ):
         dim = dataset.get_dimension(dim)
         data = dataset.data[dim.name]
         if not expanded:
             data = data.unique()
-        return data.compute().values if compute else data.values
+        if keep_index:
+            return data.compute() if compute else data
+        else:
+            return data.compute().values if compute else data.values
 
     @classmethod
     def select_mask(cls, dataset, selection):

holoviews/core/data/dictionary.py

@@ -246,7 +246,9 @@ def range(cls, dataset, dimension):
 
 
     @classmethod
-    def values(cls, dataset, dim, expanded=True, flat=True, compute=True):
+    def values(
+            cls, dataset, dim, expanded=True, flat=True, compute=True, keep_index=False
+    ):
         dim = dataset.get_dimension(dim).name
         values = dataset.data.get(dim)
         if isscalar(values):

holoviews/core/data/grid.py

@@ -338,7 +338,9 @@ def ndloc(cls, dataset, indices):
 
 
     @classmethod
-    def values(cls, dataset, dim, expanded=True, flat=True, compute=True):
+    def values(
+            cls, dataset, dim, expanded=True, flat=True, compute=True, keep_index=False
+    ):
         dim = dataset.get_dimension(dim, strict=True)
         if dim in dataset.vdims or dataset.data[dim.name].ndim > 1:
             data = dataset.data[dim.name]

holoviews/core/data/image.py

@@ -156,7 +156,9 @@ def range(cls, obj, dim):
 
 
     @classmethod
-    def values(cls, dataset, dim, expanded=True, flat=True, compute=True):
+    def values(
+            cls, dataset, dim, expanded=True, flat=True, compute=True, keep_index=False
+    ):
         """
         The set of samples available along a particular dimension.
         """

holoviews/core/data/multipath.py

@@ -281,7 +281,15 @@ def redim(cls, dataset, dimensions):
         return new_data
 
     @classmethod
-    def values(cls, dataset, dimension, expanded=True, flat=True, compute=True):
+    def values(
+            cls,
+            dataset,
+            dimension,
+            expanded=True,
+            flat=True,
+            compute=True,
+            keep_index=False,
+    ):
         """
         Returns a single concatenated array of all subpaths separated
         by NaN values. If expanded keyword is False an array of arrays
@@ -293,7 +301,9 @@ def values(cls, dataset, dimension, expanded=True, flat=True, compute=True):
         ds = cls._inner_dataset_template(dataset)
         for d in dataset.data:
             ds.data = d
-            dvals = ds.interface.values(ds, dimension, expanded, flat, compute)
+            dvals = ds.interface.values(
+                ds, dimension, expanded, flat, compute, keep_index
+            )
             if not len(dvals):
                 continue
             elif expanded:

holoviews/core/data/pandas.py

@@ -266,20 +266,33 @@ def select(cls, dataset, selection_mask=None, **selection):
         df = dataset.data
         if selection_mask is None:
             selection_mask = cls.select_mask(dataset, selection)
+
         indexed = cls.indexed(dataset, selection)
-        df = df.iloc[selection_mask]
+        if isinstance(selection_mask, pd.Series):
+            df = df[selection_mask]
+        else:
+            df = df.iloc[selection_mask]
         if indexed and len(df) == 1 and len(dataset.vdims) == 1:
             return df[dataset.vdims[0].name].iloc[0]
         return df
 
 
     @classmethod
-    def values(cls, dataset, dim, expanded=True, flat=True, compute=True):
+    def values(
+            cls,
+            dataset,
+            dim,
+            expanded=True,
+            flat=True,
+            compute=True,
+            keep_index=False,
+    ):
         dim = dataset.get_dimension(dim, strict=True)
         data = dataset.data[dim.name]
         if not expanded:
             return data.unique()
-        return data.values
+
+        return data if keep_index else data.values
 
 
     @classmethod

holoviews/core/data/xarray.py

@@ -303,7 +303,7 @@ def coords(cls, dataset, dimension, ordered=False, expanded=False, edges=False):
 
 
     @classmethod
-    def values(cls, dataset, dim, expanded=True, flat=True, compute=True):
+    def values(cls, dataset, dim, expanded=True, flat=True, compute=True, keep_index=False):
         dim = dataset.get_dimension(dim, strict=True)
         data = dataset.data[dim.name].data
         irregular = cls.irregular(dataset, dim) if dim in dataset.kdims else False

holoviews/core/dimension.py

@@ -1109,14 +1109,14 @@ def select(self, selection_specs=None, **kwargs):
             # Apply the selection on the selected object of a different type
             dimensions = selection.dimensions() + ['value']
             if any(kw in dimensions for kw in kwargs):
-                selection = selection.select(selection_specs, **kwargs)
+                selection = selection.select(selection_specs=selection_specs, **kwargs)
         elif isinstance(selection, Dimensioned) and selection._deep_indexable:
             # Apply the deep selection on each item in local selection
             items = []
             for k, v in selection.items():
                 dimensions = v.dimensions() + ['value']
                 if any(kw in dimensions for kw in kwargs):
-                    items.append((k, v.select(selection_specs, **kwargs)))
+                    items.append((k, v.select(selection_specs=selection_specs, **kwargs)))
                 else:
                     items.append((k, v))
             selection = selection.clone(items)

holoviews/core/spaces.py

@@ -1371,7 +1371,7 @@ def select(self, selection_specs=None, **kwargs):
         """
         if selection_specs is not None and not isinstance(selection_specs, (list, tuple)):
             selection_specs = [selection_specs]
-        selection = super(DynamicMap, self).select(selection_specs, **kwargs)
+        selection = super(DynamicMap, self).select(selection_specs=selection_specs, **kwargs)
         def dynamic_select(obj, **dynkwargs):
             if selection_specs is not None:
                 matches = any(obj.matches(spec) for spec in selection_specs)

holoviews/core/util.py

@@ -505,7 +505,7 @@ def process_ellipses(obj, key, vdim_selection=False):
     will be exactly one longer than the number of kdims). Note: this
     flag should not be used for composite types.
     """
-    if isinstance(key, np.ndarray) and key.dtype.kind == 'b':
+    if getattr(getattr(key, 'dtype', None), 'kind', None) == 'b':
         return key
     wrapped_key = wrap_tuple(key)
     if wrapped_key.count(Ellipsis)== 0:

holoviews/element/path.py

@@ -110,11 +110,11 @@ def __getitem__(self, key):
         return self.clone(extents=(xstart, ystart, xstop, ystop))
 
 
-    def select(self, selection_specs=None, **kwargs):
+    def select(self, *args, **kwargs):
         """
         Bypasses selection on data and sets extents based on selection.
         """
-        return super(Element2D, self).select(selection_specs, **kwargs)
+        return super(Element2D, self).select(*args, **kwargs)
 
 
     def split(self, start=None, end=None, datatype=None, **kwargs):

holoviews/plotting/util.py

@@ -477,7 +477,7 @@ def initialize_unbounded(obj, dimensions, key):
     """
     select = dict(zip([d.name for d in dimensions], key))
     try:
-        obj.select([DynamicMap], **select)
+        obj.select(selection_specs=[DynamicMap], **select)
     except KeyError:
         pass
 

holoviews/tests/core/data/base.py

@@ -11,7 +11,8 @@
 from holoviews.core.data import concat
 from holoviews.core.data.interface import DataError
 from holoviews.element import Scatter, Curve
-from holoviews.element.comparison import ComparisonTestCase 
+from holoviews.element.comparison import ComparisonTestCase
+from holoviews.util.transform import dim
 
 from collections import OrderedDict
 
@@ -697,6 +698,13 @@ def test_dataset_select_rows_gender_male(self):
                           kdims=self.kdims, vdims=self.vdims)
         self.assertEquals(row, indexed)
 
+    def test_dataset_select_rows_gender_male_expr(self):
+        row = self.table.select(selection_expr=dim('Gender') == 'M')
+        indexed = Dataset({'Gender': ['M', 'M'], 'Age': [10, 16],
+                           'Weight': [15, 18], 'Height': [0.8,0.6]},
+                          kdims=self.kdims, vdims=self.vdims)
+        self.assertEquals(row, indexed)
+
     def test_dataset_select_rows_gender_male_alias(self):
         row = self.alias_table.select(Gender='M')
         alias_row = self.alias_table.select(gender='M')
@@ -859,10 +867,24 @@ def test_dataset_scalar_select(self):
         ds = Dataset({'A': 1, 'B': np.arange(10)}, kdims=['A', 'B'])
         self.assertEqual(ds.select(A=1).dimension_values('B'), np.arange(10))
 
+    def test_dataset_scalar_select_expr(self):
+        ds = Dataset({'A': 1, 'B': np.arange(10)}, kdims=['A', 'B'])
+        self.assertEqual(
+            ds.select(selection_expr=dim('A') == 1).dimension_values('B'),
+            np.arange(10)
+        )
+
     def test_dataset_scalar_empty_select(self):
         ds = Dataset({'A': 1, 'B': np.arange(10)}, kdims=['A', 'B'])
         self.assertEqual(ds.select(A=0).dimension_values('B'), np.array([]))
 
+    def test_dataset_scalar_empty_select_expr(self):
+        ds = Dataset({'A': 1, 'B': np.arange(10)}, kdims=['A', 'B'])
+        self.assertEqual(
+            ds.select(selection_expr=dim('A') == 0).dimension_values('B'),
+            np.array([])
+        )
+
     def test_dataset_scalar_sample(self):
         ds = Dataset({'A': 1, 'B': np.arange(10)}, kdims=['A', 'B'])
         self.assertEqual(ds.sample([(1,)]).dimension_values('B'), np.arange(10))

holoviews/tests/core/data/testdaskinterface.py

@@ -9,6 +9,7 @@
     raise SkipTest("Could not import dask, skipping DaskInterface tests.")
 
 from holoviews.core.data import Dataset
+from holoviews.util.transform import dim
 
 from .testpandasinterface import PandasInterfaceTests
 
@@ -92,3 +93,16 @@ def test_dataset_range_categorical_dimension_empty(self):
         ds_range = ds.range(0)
         self.assertTrue(np.isnan(ds_range[0]))
         self.assertTrue(np.isnan(ds_range[1]))
+
+    def test_select_expression_lazy(self):
+        df = pd.DataFrame({
+            'a': [1, 2, 3, 4, 5],
+            'b': [10, 10, 11, 11, 10],
+        })
+        ddf = dd.from_pandas(df, npartitions=2)
+        ds = Dataset(ddf)
+        new_ds = ds.select(selection_expr=dim('b') == 10)
+
+        # Make sure that selecting by expression didn't cause evaluation
+        self.assertIsInstance(new_ds.data, dd.DataFrame)
+        self.assertEqual(new_ds.data.compute(), df[df.b == 10])

holoviews/tests/element/testelementselect.py

@@ -86,7 +86,9 @@ def test_deep_layout_nesting_slice(self):
         self.assertEqual(selection, hmap1 + hmap2)
 
     def test_spec_duplicate_dim_select(self):
-        selection = self.duplicate_map.select((HoloMap,), x=(0, 1), y=(1, 3))
+        selection = self.duplicate_map.select(
+            selection_specs=(HoloMap,), x=(0, 1), y=(1, 3)
+        )
         self.assertEqual(selection, self.duplicate_map[0:1, 1:3])
 
     def test_duplicate_dim_select(self):
@@ -102,11 +104,20 @@ def test_datetime_select(self):
         curve = self.datetime_fn()
         overlay = curve * self.datetime_fn()
         for el in [curve, overlay]:
-            self.assertEqual(el.select(time=(s, e)), el[s:e])
+            v = el.select(time=(s, e))
+            self.assertEqual(v, el[s:e])
             self.assertEqual(el.select(time=
                 (dt.datetime(1999, 12, 31), dt.datetime(2000, 1, 2))), el[s:e]
             )
             if pd:
                 self.assertEqual(el.select(
                     time=(pd.Timestamp(s), pd.Timestamp(e))
                 ), el[pd.Timestamp(s):pd.Timestamp(e)])
+
+    def test_selection_spec_positional_error_message(self):
+        s, e = '1999-12-31', '2000-1-2'
+        curve = self.datetime_fn()
+        with self.assertRaisesRegexp(
+                ValueError, "Use the selection_specs keyword"
+        ):
+            curve.select((Curve,), time=(s, e))