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"""
Base class for ensemble-based estimators.
"""
# Authors: Gilles Louppe
# License: BSD 3 clause
import numpy as np
from ..base import clone
from ..base import BaseEstimator
from ..base import MetaEstimatorMixin
from ..utils import _get_n_jobs, check_random_state
MAX_RAND_SEED = np.iinfo(np.int32).max
def _set_random_states(estimator, random_state=None):
"""Sets fixed random_state parameters for an estimator
Finds all parameters ending ``random_state`` and sets them to integers
derived from ``random_state``.
Parameters
----------
estimator : estimator supporting get/set_params
Estimator with potential randomness managed by random_state
parameters.
random_state : numpy.RandomState or int, optional
Random state used to generate integer values.
Notes
-----
This does not necessarily set *all* ``random_state`` attributes that
control an estimator's randomness, only those accessible through
``estimator.get_params()``. ``random_state``s not controlled include
those belonging to:
* cross-validation splitters
* ``scipy.stats`` rvs
"""
random_state = check_random_state(random_state)
to_set = {}
for key in sorted(estimator.get_params(deep=True)):
if key == 'random_state' or key.endswith('__random_state'):
to_set[key] = random_state.randint(MAX_RAND_SEED)
if to_set:
estimator.set_params(**to_set)
class BaseEnsemble(BaseEstimator, MetaEstimatorMixin):
"""Base class for all ensemble classes.
Warning: This class should not be used directly. Use derived classes
instead.
Parameters
----------
base_estimator : object, optional (default=None)
The base estimator from which the ensemble is built.
n_estimators : integer
The number of estimators in the ensemble.
estimator_params : list of strings
The list of attributes to use as parameters when instantiating a
new base estimator. If none are given, default parameters are used.
Attributes
----------
base_estimator_ : estimator
The base estimator from which the ensemble is grown.
estimators_ : list of estimators
The collection of fitted base estimators.
"""
def __init__(self, base_estimator, n_estimators=10,
estimator_params=tuple()):
# Set parameters
self.base_estimator = base_estimator
self.n_estimators = n_estimators
self.estimator_params = estimator_params
# Don't instantiate estimators now! Parameters of base_estimator might
# still change. Eg., when grid-searching with the nested object syntax.
# This needs to be filled by the derived classes.
self.estimators_ = []
def _validate_estimator(self, default=None):
"""Check the estimator and the n_estimator attribute, set the
`base_estimator_` attribute."""
if self.n_estimators <= 0:
raise ValueError("n_estimators must be greater than zero, "
"got {0}.".format(self.n_estimators))
if self.base_estimator is not None:
self.base_estimator_ = self.base_estimator
else:
self.base_estimator_ = default
if self.base_estimator_ is None:
raise ValueError("base_estimator cannot be None")
def _make_estimator(self, append=True, random_state=None):
"""Make and configure a copy of the `base_estimator_` attribute.
Warning: This method should be used to properly instantiate new
sub-estimators.
"""
estimator = clone(self.base_estimator_)
estimator.set_params(**dict((p, getattr(self, p))
for p in self.estimator_params))
if random_state is not None:
_set_random_states(estimator, random_state)
if append:
self.estimators_.append(estimator)
return estimator
def __len__(self):
"""Returns the number of estimators in the ensemble."""
return len(self.estimators_)
def __getitem__(self, index):
"""Returns the index'th estimator in the ensemble."""
return self.estimators_[index]
def __iter__(self):
"""Returns iterator over estimators in the ensemble."""
return iter(self.estimators_)
def _partition_estimators(n_estimators, n_jobs):
"""Private function used to partition estimators between jobs."""
# Compute the number of jobs
n_jobs = min(_get_n_jobs(n_jobs), n_estimators)
# Partition estimators between jobs
n_estimators_per_job = (n_estimators // n_jobs) * np.ones(n_jobs,
dtype=np.int)
n_estimators_per_job[:n_estimators % n_jobs] += 1
starts = np.cumsum(n_estimators_per_job)
return n_jobs, n_estimators_per_job.tolist(), [0] + starts.tolist()
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