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Jun 22, 2013
Merged

MRG allow empty grid in ParameterGrid #2082

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0c3ae9c
ENH allow empty grid in ParameterGrid
larsmans Jun 21, 2013
fe2aad9
DOC ParameterGrid on lists
larsmans Jun 22, 2013
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29 changes: 22 additions & 7 deletions sklearn/grid_search.py
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Original file line number Diff line number Diff line change
Expand Up @@ -43,18 +43,30 @@ class ParameterGrid(object):

Parameters
----------
param_grid : dict of string to sequence
param_grid : dict of string to sequence, or sequence of such
The parameter grid to explore, as a dictionary mapping estimator
parameters to sequences of allowed values.

An empty dict signifies default parameters.

A sequence of dicts signifies a sequence of grids to search, and is
useful to avoid exploring parameter combinations that make no sense
or have no effect. See the examples below.

Examples
--------
>>> from sklearn.grid_search import ParameterGrid
>>> param_grid = {'a':[1, 2], 'b':[True, False]}
>>> param_grid = {'a': [1, 2], 'b': [True, False]}
>>> list(ParameterGrid(param_grid)) #doctest: +NORMALIZE_WHITESPACE
[{'a': 1, 'b': True}, {'a': 1, 'b': False},
{'a': 2, 'b': True}, {'a': 2, 'b': False}]

>>> grid = [{'kernel': ['linear']}, {'kernel': ['rbf'], 'gamma': [1, 10]}]
>>> list(ParameterGrid(grid)) #doctest: +NORMALIZE_WHITESPACE
[{'kernel': 'linear'},
{'kernel': 'rbf', 'gamma': 1},
{'kernel': 'rbf', 'gamma': 10}]

See also
--------
:class:`GridSearchCV`:
Expand All @@ -81,16 +93,19 @@ def __iter__(self):
for p in self.param_grid:
# Always sort the keys of a dictionary, for reproducibility
items = sorted(p.items())
keys, values = zip(*items)
for v in product(*values):
params = dict(zip(keys, v))
yield params
if not items:
yield {}
else:
keys, values = zip(*items)
for v in product(*values):
params = dict(zip(keys, v))
yield params

def __len__(self):
"""Number of points on the grid."""
# Product function that can handle iterables (np.product can't).
product = partial(reduce, operator.mul)
return sum(product(len(v) for v in p.values())
return sum(product(len(v) for v in p.values()) if p else 1
for p in self.param_grid)


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9 changes: 9 additions & 0 deletions sklearn/tests/test_grid_search.py
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Expand Up @@ -130,6 +130,15 @@ def test_parameter_grid():
set(("foo", x, "bar", y)
for x, y in product(params2["foo"], params2["bar"])))

# Special case: empty grid (useful to get default estimator settings)
empty = ParameterGrid({})
assert_equal(len(empty), 1)
assert_equal(list(empty), [{}])

has_empty = ParameterGrid([{'C': [1, 10]}, {}])
assert_equal(len(has_empty), 3)
assert_equal(list(has_empty), [{'C': 1}, {'C': 10}, {}])


def test_grid_search():
"""Test that the best estimator contains the right value for foo_param"""
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