remove fuse_selections

dask/optimization.py

@@ -376,53 +376,6 @@ def functions_of(task):
     return funcs
 
 
-def fuse_selections(dsk, head1, head2, merge):
-    """Fuse selections with lower operation.
-
-    Handles graphs of the form:
-    ``{key1: (head1, key2, ...), key2: (head2, ...)}``
-
-    Parameters
-    ----------
-    dsk : dict
-        dask graph
-    head1 : function
-        The first element of task1
-    head2 : function
-        The first element of task2
-    merge : function
-        Takes ``task1`` and ``task2`` and returns a merged task to
-        replace ``task1``.
-
-    Examples
-    --------
-    >>> def load(store, partition, columns):
-    ...     pass
-    >>> dsk = {'x': (load, 'store', 'part', ['a', 'b']),
-    ...        'y': (getitem, 'x', 'a')}
-    >>> merge = lambda t1, t2: (load, t2[1], t2[2], t1[2])
-    >>> dsk2 = fuse_selections(dsk, getitem, load, merge)
-    >>> cull(dsk2, 'y')[0]
-    {'y': (<function load at ...>, 'store', 'part', 'a')}
-    """
-    dsk2 = dict()
-    for k, v in dsk.items():
-        try:
-            if (
-                istask(v)
-                and v[0] == head1
-                and v[1] in dsk
-                and istask(dsk[v[1]])
-                and dsk[v[1]][0] == head2
-            ):
-                dsk2[k] = merge(v, dsk[v[1]])
-            else:
-                dsk2[k] = v
-        except TypeError:
-            dsk2[k] = v
-    return dsk2
-
-
 def default_fused_keys_renamer(keys):
     """Create new keys for ``fuse`` tasks"""
     it = reversed(keys)

dask/tests/test_optimization.py

@@ -1,6 +1,5 @@
 import itertools
 import pickle
-from operator import getitem
 from functools import partial
 
 import pytest
@@ -14,7 +13,6 @@
     inline,
     inline_functions,
     functions_of,
-    fuse_selections,
     fuse_linear,
     SubgraphCallable,
 )
@@ -306,17 +304,6 @@ def test_functions_of():
     assert functions_of((a,)) == set([a])
 
 
-def test_fuse_selections():
-    def load(*args):
-        pass
-
-    dsk = {"x": (load, "store", "part", ["a", "b"]), "y": (getitem, "x", "a")}
-    merge = lambda t1, t2: (load, t2[1], t2[2], t1[2])
-    dsk2 = fuse_selections(dsk, getitem, load, merge)
-    dsk2, dependencies = cull(dsk2, "y")
-    assert dsk2 == {"y": (load, "store", "part", "a")}
-
-
 def test_inline_cull_dependencies():
     d = {"a": 1, "b": "a", "c": "b", "d": ["a", "b", "c"], "e": (add, (len, "d"), "a")}