"""Random Search Optimizer."""
from skopt import Space
from evalml.tuners import NoParamsException, Tuner
from evalml.utils import get_random_state
[docs]class RandomSearchTuner(Tuner):
"""Random Search Optimizer.
Args:
pipeline_hyperparameter_ranges (dict): a set of hyperparameter ranges corresponding to a pipeline's parameters
with_replacement (bool): If false, only unique hyperparameters will be shown
replacement_max_attempts (int): The maximum number of tries to get a unique
set of random parameters. Only used if tuner is initalized with
with_replacement=True
random_seed (int): Seed for random number generator. Defaults to 0.
Example:
>>> tuner = RandomSearchTuner({'My Component': {'param a': [0.0, 10.0], 'param b': ['a', 'b', 'c']}}, random_seed=42)
>>> proposal = tuner.propose()
>>> assert proposal.keys() == {'My Component'}
>>> assert proposal['My Component'] == {'param a': 3.7454011884736254, 'param b': 'c'}
"""
def __init__(
self,
pipeline_hyperparameter_ranges,
with_replacement=False,
replacement_max_attempts=10,
random_seed=0,
):
super().__init__(pipeline_hyperparameter_ranges, random_seed=random_seed)
self._space = Space(self._search_space_ranges)
self._random_state = get_random_state(random_seed)
self._with_replacement = with_replacement
self._replacement_max_attempts = replacement_max_attempts
self._used_parameters = set()
self._used_parameters.add(())
self.curr_params = None
[docs] def add(self, pipeline_parameters, score):
"""Not applicable to random search tuner as generated parameters are not dependent on scores of previous parameters.
Args:
pipeline_parameters (dict): A dict of the parameters used to evaluate a pipeline
score (float): The score obtained by evaluating the pipeline with the provided parameters
"""
pass
def _get_sample(self):
return tuple(self._space.rvs(random_state=self._random_state)[0])
[docs] def propose(self):
"""Generate a unique set of parameters.
If tuner was initialized with ``with_replacement=True`` and the tuner is unable to
generate a unique set of parameters after ``replacement_max_attempts`` tries, then ``NoParamsException`` is raised.
Returns:
dict: Proposed pipeline parameters
"""
if not len(self._search_space_ranges):
return self._convert_to_pipeline_parameters({})
if self._with_replacement:
return self._convert_to_pipeline_parameters(self._get_sample())
elif not self.curr_params:
self.is_search_space_exhausted()
params = self.curr_params
self.curr_params = None
return self._convert_to_pipeline_parameters(params)
[docs] def is_search_space_exhausted(self):
"""Checks if it is possible to generate a set of valid parameters. Stores generated parameters in ``self.curr_params`` to be returned by ``propose()``.
Returns:
bool: If no more valid parameters exists in the search space, return False.
Raises:
NoParamsException: If a search space is exhausted, then this exception is thrown.
"""
if self._with_replacement:
return False
else:
curr_params = ()
attempts = 0
while curr_params in self._used_parameters:
if attempts >= self._replacement_max_attempts:
raise NoParamsException(
"Cannot create a unique set of unexplored parameters. Try expanding the search space."
)
return True
attempts += 1
curr_params = self._get_sample()
self._used_parameters.add(curr_params)
self.curr_params = curr_params
return False