# Source code for econml.policy._forest._tree

# Copyright (c) Microsoft Corporation. All rights reserved.
#
# This code contains snippets of code from:
# https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/tree/_classes.py
#
# Copyright (c) 2007-2020 The scikit-learn developers.

import numpy as np
import numbers
from math import ceil
from ...tree import Tree
from ...tree._criterion import Criterion
from ...tree._splitter import Splitter, BestSplitter
from ...tree import DepthFirstTreeBuilder
from ...tree import _tree
from ..._tree_exporter import _SingleTreeExporterMixin, _PolicyTreeDOTExporter, _PolicyTreeMPLExporter
from ._criterion import LinearPolicyCriterion
from . import _criterion
from ...tree import BaseTree
from sklearn.model_selection import train_test_split
from sklearn.utils import check_array, check_X_y
from sklearn.utils import check_random_state
from sklearn.utils.validation import _check_sample_weight
from sklearn.utils.validation import check_is_fitted
import copy

# =============================================================================
# Types and constants
# =============================================================================

CRITERIA_POLICY = {"neg_welfare": LinearPolicyCriterion}

# =============================================================================
# Base Policy tree
# =============================================================================

[docs]class PolicyTree(_SingleTreeExporterMixin, BaseTree):
""" Welfare maximization policy tree. Trains a tree to maximize the objective:
:math:1/n \\sum_i \\sum_j a_j(X_i) * y_{ij}, where, where :math:a(X) is constrained
to take value of 1 only on one coordinate and zero otherwise. This corresponds to a policy
optimization problem.

Parameters
----------
criterion : {'neg_welfare'}, default='neg_welfare'
The criterion type

splitter : {"best"}, default="best"
The strategy used to choose the split at each node. Supported
strategies are "best" to choose the best split.

max_depth : int, default=None
The maximum depth of the tree. If None, then nodes are expanded until
all leaves are pure or until all leaves contain less than
min_samples_split samples.

min_samples_split : int or float, default=10
The minimum number of samples required to split an internal node:

- If int, then consider min_samples_split as the minimum number.
- If float, then min_samples_split is a fraction and
ceil(min_samples_split * n_samples) are the minimum
number of samples for each split.

min_samples_leaf : int or float, default=5
The minimum number of samples required to be at a leaf node.
A split point at any depth will only be considered if it leaves at
least min_samples_leaf training samples in each of the left and
right branches.  This may have the effect of smoothing the model,
especially in regression.

- If int, then consider min_samples_leaf as the minimum number.
- If float, then min_samples_leaf is a fraction and
ceil(min_samples_leaf * n_samples) are the minimum
number of samples for each node.

min_weight_fraction_leaf : float, default=0.0
The minimum weighted fraction of the sum total of weights (of all
the input samples) required to be at a leaf node. Samples have
equal weight when sample_weight is not provided.

max_features : int, float or {"auto", "sqrt", "log2"}, default=None
The number of features to consider when looking for the best split:

- If int, then consider max_features features at each split.
- If float, then max_features is a fraction and
int(max_features * n_features) features are considered at each
split.
- If "auto", then max_features=n_features.
- If "sqrt", then max_features=sqrt(n_features).
- If "log2", then max_features=log2(n_features).
- If None, then max_features=n_features.

Note: the search for a split does not stop until at least one
valid partition of the node samples is found, even if it requires to
effectively inspect more than max_features features.

random_state : int, RandomState instance or None, default=None
Controls the randomness of the estimator. The features are always
randomly permuted at each split, even if splitter is set to
"best". When max_features < n_features, the algorithm will
select max_features at random at each split before finding the best
split among them. But the best found split may vary across different
runs, even if max_features=n_features. That is the case, if the
improvement of the criterion is identical for several splits and one
split has to be selected at random. To obtain a deterministic behaviour
during fitting, random_state has to be fixed to an integer.

min_impurity_decrease : float, default=0.0
A node will be split if this split induces a decrease of the impurity
greater than or equal to this value.
The weighted impurity decrease equation is the following::

N_t / N * (impurity - N_t_R / N_t * right_impurity
- N_t_L / N_t * left_impurity)

where N is the total number of samples, N_t is the number of
samples at the current node, N_t_L is the number of samples in the
left child, and N_t_R is the number of samples in the right child.
N, N_t, N_t_R and N_t_L all refer to the weighted sum,
if sample_weight is passed.

min_balancedness_tol: float in [0, .5], default=.45
How imbalanced a split we can tolerate. This enforces that each split leaves at least
(.5 - min_balancedness_tol) fraction of samples on each side of the split; or fraction
of the total weight of samples, when sample_weight is not None. Default value, ensures
that at least 5% of the parent node weight falls in each side of the split. Set it to 0.0 for no
balancedness and to .5 for perfectly balanced splits. For the formal inference theory
to be valid, this has to be any positive constant bounded away from zero.

honest: bool, default=True
Whether the data should be split in two equally sized samples, such that the one half-sample
is used to determine the optimal split at each node and the other sample is used to determine
the value of every node.

Attributes
----------
feature_importances_ : ndarray of shape (n_features,)
The feature importances based on the amount of parameter heterogeneity they create.
The higher, the more important the feature.

max_features_ : int
The inferred value of max_features.

n_features_ : int
The number of features when fit is performed.

n_samples_ : int
The number of training samples when fit is performed.

honest_ : int
Whether honesty was enabled when fit was performed

tree_ : Tree instance
The underlying Tree object. Please refer to
help(econml.tree._tree.Tree) for attributes of Tree object.

policy_value_ : float
The value achieved by the recommended policy

always_treat_value_ : float
The value of the policy that treats all samples

"""

[docs]    def __init__(self, *,
criterion='neg_welfare',
splitter="best",
max_depth=None,
min_samples_split=10,
min_samples_leaf=5,
min_weight_fraction_leaf=0.,
max_features=None,
random_state=None,
min_impurity_decrease=0.,
min_balancedness_tol=0.45,
honest=True):
super().__init__(criterion=criterion,
splitter=splitter,
max_depth=max_depth,
min_samples_split=min_samples_split,
min_samples_leaf=min_samples_leaf,
min_weight_fraction_leaf=min_weight_fraction_leaf,
max_features=max_features,
random_state=random_state,
min_impurity_decrease=min_impurity_decrease,
min_balancedness_tol=min_balancedness_tol,
honest=honest)

def _get_valid_criteria(self):
return CRITERIA_POLICY

def _get_store_jac(self):
return False

def init(self,):
return self

[docs]    def fit(self, X, y, *, sample_weight=None, check_input=True):
""" Fit the tree from the data

Parameters
----------
X : (n, n_features) array
The features to split on

y : (n, n_treatments) array
The reward for each of the m treatments (including baseline treatment)

sample_weight : (n,) array, default=None
The sample weights

check_input : bool, defaul=True
Whether to check the input parameters for validity. Should be set to False to improve
running time in parallel execution, if the variables have already been checked by the
forest class that spawned this tree.

Returns
-------
self : object instance
"""

self.random_seed_ = self.random_state
self.random_state_ = check_random_state(self.random_seed_)
if check_input:
X, y = check_X_y(X, y, multi_output=True, y_numeric=True, ensure_min_features=0)
n_y = 1 if y.ndim == 1 else y.shape
super().fit(X, y, n_y, n_y, n_y,
sample_weight=sample_weight, check_input=check_input)

# The values below are required and utilitized by methods in the _SingleTreeExporterMixin
self.tree_model_ = self
self.policy_value_ = np.mean(np.max(self.predict_value(X), axis=1))
self.always_treat_value_ = np.mean(y, axis=0)
return self

[docs]    def predict(self, X, check_input=True):
""" Predict the best treatment for each sample

Parameters
----------
X : {array-like} of shape (n_samples, n_features)
The input samples. Internally, it will be converted to
dtype=np.float64.
check_input : bool, default=True
Allow to bypass several input checking.
Don't use this parameter unless you know what you do.

Returns
-------
treatment : array-like of shape (n_samples)
The recommded treatment, i.e. the treatment index with the largest reward for each sample
"""
check_is_fitted(self)
X = self._validate_X_predict(X, check_input)
pred = self.tree_.predict(X)
return np.argmax(pred, axis=1)

[docs]    def predict_proba(self, X, check_input=True):
""" Predict the probability of recommending each treatment

Parameters
----------
X : {array-like} of shape (n_samples, n_features)
The input samples. Internally, it will be converted to
dtype=np.float64.
check_input : bool, default=True
Allow to bypass several input checking.
Don't use this parameter unless you know what you do.

Returns
-------
treatment_proba : array-like of shape (n_samples, n_treatments)
The probability of each treatment recommendation
"""
check_is_fitted(self)
X = self._validate_X_predict(X, check_input)
pred = self.tree_.predict(X)
proba = np.zeros(pred.shape)
proba[np.arange(X.shape), np.argmax(pred, axis=1)] = 1
return proba

[docs]    def predict_value(self, X, check_input=True):
""" Predict the expected value of each treatment for each sample

Parameters
----------
X : {array-like} of shape (n_samples, n_features)
The input samples. Internally, it will be converted to
dtype=np.float64.
check_input : bool, default=True
Allow to bypass several input checking.
Don't use this parameter unless you know what you do.

Returns
-------
welfare : array-like of shape (n_samples, n_treatments)
The conditional average welfare for each treatment for the group of each sample defined by the tree
"""
check_is_fitted(self)
X = self._validate_X_predict(X, check_input)
pred = self.tree_.predict(X)
return pred

[docs]    def feature_importances(self, max_depth=4, depth_decay_exponent=2.0):
"""

Parameters
----------
max_depth : int, default=4
Splits of depth larger than max_depth are not used in this calculation
depth_decay_exponent: double, default=2.0
The contribution of each split to the total score is re-weighted by 1 / (1 + depth)**2.0.

Returns
-------
feature_importances_ : ndarray of shape (n_features,)
Normalized total parameter heterogeneity inducing importance of each feature
"""
check_is_fitted(self)

return self.tree_.compute_feature_importances(normalize=True, max_depth=max_depth,
depth_decay=depth_decay_exponent)

@property
def feature_importances_(self):
return self.feature_importances()

def _make_dot_exporter(self, *, out_file, feature_names, treatment_names, max_depth, filled,
leaves_parallel, rotate, rounded,
special_characters, precision):
title = "Average policy gains over no treatment: {} \n".format(np.around(self.policy_value_, precision))
title += "Average policy gains over constant treatment policies for each treatment: {}".format(
np.around(self.policy_value_ - self.always_treat_value_, precision))
return _PolicyTreeDOTExporter(out_file=out_file, title=title,
treatment_names=treatment_names, feature_names=feature_names,
max_depth=max_depth,
filled=filled, leaves_parallel=leaves_parallel, rotate=rotate,
rounded=rounded, special_characters=special_characters,
precision=precision)

def _make_mpl_exporter(self, *, title, feature_names, treatment_names, max_depth, filled,
rounded, precision, fontsize):
title = "" if title is None else title
title += "Average policy gains over no treatment: {} \n".format(np.around(self.policy_value_, precision))
title += "Average policy gains over constant treatment policies for each treatment: {}".format(
np.around(self.policy_value_ - self.always_treat_value_, precision))
return _PolicyTreeMPLExporter(treatment_names=treatment_names, title=title,
feature_names=feature_names, max_depth=max_depth,
filled=filled,
rounded=rounded,
precision=precision, fontsize=fontsize)