Greedy rule list. Greedily splits on one feature at a time along a single path.

Expand source code
'''Greedy rule list. Greedily splits on one feature at a time along a single path.
'''

import math
from copy import deepcopy

import numpy as np
from sklearn.base import BaseEstimator, ClassifierMixin
from sklearn.utils.multiclass import unique_labels
from sklearn.utils.validation import check_array, check_is_fitted

from imodels.rule_list.rule_list import RuleList


class GreedyRuleListClassifier(BaseEstimator, RuleList, ClassifierMixin):
    def __init__(self, max_depth: int = 5, class_weight=None, criterion: str = 'gini', strategy: str = 'max'):
        '''
        Params
        ------
        max_depth
            Maximum depth the list can achieve
        criterion: str
            Criterion used to split
            'gini', 'entropy', or 'neg_corr'
        strategy: str
            How to select which side of split becomes leaf node
            Currently only supports 'max' - (higher risk side of split becomes leaf node)
        '''

        self.max_depth = max_depth
        self.class_weight = class_weight
        self.criterion = criterion
        self.strategy = strategy
        self.depth = 0  # tracks the fitted depth
        self._estimator_type = 'classifier'

    def fit(self, X, y, depth: int = 0, feature_names=None, verbose=False):
        """
        Params
        ------
        X: array_like
            Feature set
        y: array_like
            target variable
        depth
            the depth of the current layer (used to recurse)
        """

        # set self.feature_names and make sure X, y are not pandas type
        if 'pandas' in str(type(X)):
            X = X.values
        else:
            if feature_names is None:
                self.feature_names_ = ['feat ' + str(i) for i in range(X.shape[1])]
        if feature_names is not None:
            self.feature_names_ = feature_names

        # base case 1: no data in this group
        if len(y) == 0:
            return []

        # base case 2: all y is the same in this group
        elif self._all_same(y):
            return [{'val': y[0], 'num_pts': y.size}]

        # base case 3: max depth reached 
        elif depth >= self.max_depth:
            return []

        # recursively generate rule list 
        else:

            # find a split with the best value for the criterion
            col, cutoff, criterion_val = self._find_best_split(X, y)

            # put higher probability of class 1 on the right-hand side
            if self.strategy == 'max':
                y_left = y[X[:, col] < cutoff]  # left-hand side data
                y_right = y[X[:, col] >= cutoff]  # right-hand side data
                if len(y_left) > 0 and np.mean(y_left) > np.mean(y_right):
                    flip = True
                    tmp = deepcopy(y_left)
                    y_left = deepcopy(y_right)
                    y_right = tmp
                    x_left = X[X[:, col] >= cutoff]
                else:
                    flip = False
                    x_left = X[X[:, col] < cutoff]
            else:
                print('strategy must be max!')

            # print
            if verbose:
                print(
                    f'{np.mean(100 * y):.2f} -> {self.feature_names_[col]} -> {np.mean(100 * y_left):.2f} ({y_left.size}) {np.mean(100 * y_right):.2f} ({y_right.size})')

            # save info
            par_node = [{
                'col': self.feature_names_[col],
                'index_col': col,
                'cutoff': cutoff,
                'val': np.mean(y),  # values before splitting
                'flip': flip,
                'val_right': np.mean(y_right),
                'num_pts': y.size,
                'num_pts_right': y_right.size
            }]

            # generate tree for the non-leaf data
            par_node = par_node + self.fit(x_left, y_left, depth + 1, feature_names=feature_names, verbose=verbose)

            self.depth += 1  # increase the depth since we call fit once
            self.rules_ = par_node
            self.complexity_ = len(self.rules_)
            self.classes_ = unique_labels(y)
            return par_node

    def predict_proba(self, X):
        check_is_fitted(self)
        X = check_array(X)
        n = X.shape[0]
        probs = np.zeros(n)
        for i in range(n):
            x = X[i]
            for j, rule in enumerate(self.rules_):
                if j == len(self.rules_) - 1:
                    probs[i] = rule['val']
                elif x[rule['index_col']] >= rule['cutoff']:
                    probs[i] = rule['val_right']
                    break
        return np.vstack((1 - probs, probs)).transpose()  # probs (n, 2)

    def predict(self, X):
        check_is_fitted(self)
        X = check_array(X)
        return np.argmax(self.predict_proba(X), axis=1)

    def __str__(self):
        s = ''
        for rule in self.rules_:
            s += f"mean {rule['val'].round(3)} ({rule['num_pts']} pts)\n"
            if 'col' in rule:
                s += f"if {rule['col']} >= {rule['cutoff']} then {rule['val_right'].round(3)} ({rule['num_pts_right']} pts)\n"
        return s

    def _print_list(self):
        '''Print out the list in a nice way
        '''
        s = ''

        def red(s):
            return f"\033[91m{s}\033[00m"

        def cyan(s):
            return f"\033[96m{s}\033[00m"

        def rule_name(rule):
            if rule['flip']:
                return '~' + rule['col']
            return rule['col']

        # rule = self.rules_[0]
        #     s += f"{red((100 * rule['val']).round(3))}% IwI ({rule['num_pts']} pts)\n"
        for rule in self.rules_:
            s += f"\t{'':>35} => {cyan((100 * rule['val']).round(2)):>6}% risk ({rule['num_pts']} pts)\n"
            #         s += f"\t{'Else':>45} => {cyan((100 * rule['val']).round(2)):>6}% IwI ({rule['val'] * rule['num_pts']:.0f}/{rule['num_pts']} pts)\n"
            if 'col' in rule:
                #             prefix = f"if {rule['col']} >= {rule['cutoff']}"
                prefix = f"if {rule_name(rule)}"
                val = f"{100 * rule['val_right'].round(3):.4}"
                s += f"{prefix:>43} ===> {red(val)}% risk ({rule['num_pts_right']} pts)\n"
        # rule = self.rules_[-1]
        #     s += f"{red((100 * rule['val']).round(3))}% IwI ({rule['num_pts']} pts)\n"
        print(s)

    def _all_same(self, items):
        return all(x == items[0] for x in items)

    def _find_best_split(self, x, y):
        """
        Find the best split from all features
        returns: the column to split on, the cutoff value, and the actual criterion_value
        """
        col = None
        min_criterion_val = 1e10
        cutoff = None

        # iterating through each feature
        for i, c in enumerate(x.T):

            # find the best split of that feature
            criterion_val, cur_cutoff = self._split_on_feature(c, y)

            # found perfect cutoff
            if criterion_val == 0:
                return i, cur_cutoff, criterion_val

            # check if it's best so far
            elif criterion_val <= min_criterion_val:
                min_criterion_val = criterion_val
                col = i
                cutoff = cur_cutoff
        return col, cutoff, min_criterion_val

    def _split_on_feature(self, col, y):
        """
        col: the column we split on
        y: target var
        """
        min_criterion_val = 1e10
        cutoff = 0.5

        # iterate through each value in the column
        for value in np.unique(col):
            # separate y into 2 groups
            y_predict = col < value

            # get criterion val of this split
            criterion_val = self._weighted_criterion(y_predict, y)

            # check if it's the smallest one so far
            if criterion_val <= min_criterion_val:
                min_criterion_val = criterion_val
                cutoff = value
        return min_criterion_val, cutoff

    def _weighted_criterion(self, split_decision, y_real):
        """Returns criterion calculated over a split
        split decision, True/False, and y_true can be multi class
        """
        if split_decision.shape[0] != y_real.shape[0]:
            print('They have to be the same length')
            return None

        # choose the splitting criterion
        if self.criterion == 'entropy':
            criterion_func = self._entropy_criterion
        elif self.criterion == 'gini':
            criterion_func = self._gini_criterion
        elif self.criterion == 'neg_corr':
            return self._neg_corr_criterion(split_decision, y_real)

        # left-hand side criterion
        s_left = criterion_func(y_real[split_decision])

        # right-hand side criterion
        s_right = criterion_func(y_real[~split_decision])

        # overall criterion, again weighted average
        n = y_real.shape[0]
        if self.class_weight is not None:
            sample_weights = np.ones(n)
            for c in self.class_weight.keys():
                idxs_c = y_real == c
                sample_weights[idxs_c] = self.class_weight[c]
            total_weight = np.sum(sample_weights)
            weight_left = np.sum(sample_weights[split_decision]) / total_weight
            # weight_right = np.sum(sample_weights[~split_decision]) / total_weight
        else:
            tot_left_samples = np.sum(split_decision == 1)
            weight_left = tot_left_samples / n

        s = weight_left * s_left + (1 - weight_left) * s_right
        return s

    def _gini_criterion(self, y):
        '''Returns gini index for one node
        = sum(pc * (1 – pc))
        '''
        s = 0
        n = y.shape[0]
        classes = np.unique(y)

        # for each class, get entropy
        for c in classes:
            # weights for each class
            n_c = np.sum(y == c)
            p_c = n_c / n

            # weighted avg
            s += p_c * (1 - p_c)

        return s

    def _entropy_criterion(self, y):
        """Returns entropy of a divided group of data
        Data may have multiple classes
        """
        s = 0
        n = len(y)
        classes = set(y)

        # for each class, get entropy
        for c in classes:
            # weights for each class
            weight = sum(y == c) / n

            def _entropy_from_counts(c1, c2):
                """Returns entropy of a group of data
                c1: count of one class
                c2: count of another class
                """
                if c1 == 0 or c2 == 0:  # when there is only one class in the group, entropy is 0
                    return 0

                def _entropy_func(p): return -p * math.log(p, 2)

                p1 = c1 * 1.0 / (c1 + c2)
                p2 = c2 * 1.0 / (c1 + c2)
                return _entropy_func(p1) + _entropy_func(p2)

            # weighted avg
            s += weight * _entropy_from_counts(sum(y == c), sum(y != c))
        return s

    def _neg_corr_criterion(self, split_decision, y):
        '''Returns negative correlation between y
        and the binary splitting variable split_decision
        y must be binary
        '''
        if np.unique(y).size < 2:
            return 0
        elif np.unique(y).size != 2:
            print('y must be binary output for corr criterion')

        # y should be 1 more often on the "right side" of the split
        if y.sum() < y.size / 2:
            y = 1 - y

        return -1 * np.corrcoef(split_decision.astype(np.int), y)[0, 1]

Classes

class GreedyRuleListClassifier (max_depth: int = 5, class_weight=None, criterion: str = 'gini', strategy: str = 'max')

Base class for all estimators in scikit-learn.

Notes

All estimators should specify all the parameters that can be set at the class level in their __init__ as explicit keyword arguments (no *args or **kwargs).

Params

max_depth Maximum depth the list can achieve criterion: str Criterion used to split 'gini', 'entropy', or 'neg_corr' strategy: str How to select which side of split becomes leaf node Currently only supports 'max' - (higher risk side of split becomes leaf node)

Expand source code
class GreedyRuleListClassifier(BaseEstimator, RuleList, ClassifierMixin):
    def __init__(self, max_depth: int = 5, class_weight=None, criterion: str = 'gini', strategy: str = 'max'):
        '''
        Params
        ------
        max_depth
            Maximum depth the list can achieve
        criterion: str
            Criterion used to split
            'gini', 'entropy', or 'neg_corr'
        strategy: str
            How to select which side of split becomes leaf node
            Currently only supports 'max' - (higher risk side of split becomes leaf node)
        '''

        self.max_depth = max_depth
        self.class_weight = class_weight
        self.criterion = criterion
        self.strategy = strategy
        self.depth = 0  # tracks the fitted depth
        self._estimator_type = 'classifier'

    def fit(self, X, y, depth: int = 0, feature_names=None, verbose=False):
        """
        Params
        ------
        X: array_like
            Feature set
        y: array_like
            target variable
        depth
            the depth of the current layer (used to recurse)
        """

        # set self.feature_names and make sure X, y are not pandas type
        if 'pandas' in str(type(X)):
            X = X.values
        else:
            if feature_names is None:
                self.feature_names_ = ['feat ' + str(i) for i in range(X.shape[1])]
        if feature_names is not None:
            self.feature_names_ = feature_names

        # base case 1: no data in this group
        if len(y) == 0:
            return []

        # base case 2: all y is the same in this group
        elif self._all_same(y):
            return [{'val': y[0], 'num_pts': y.size}]

        # base case 3: max depth reached 
        elif depth >= self.max_depth:
            return []

        # recursively generate rule list 
        else:

            # find a split with the best value for the criterion
            col, cutoff, criterion_val = self._find_best_split(X, y)

            # put higher probability of class 1 on the right-hand side
            if self.strategy == 'max':
                y_left = y[X[:, col] < cutoff]  # left-hand side data
                y_right = y[X[:, col] >= cutoff]  # right-hand side data
                if len(y_left) > 0 and np.mean(y_left) > np.mean(y_right):
                    flip = True
                    tmp = deepcopy(y_left)
                    y_left = deepcopy(y_right)
                    y_right = tmp
                    x_left = X[X[:, col] >= cutoff]
                else:
                    flip = False
                    x_left = X[X[:, col] < cutoff]
            else:
                print('strategy must be max!')

            # print
            if verbose:
                print(
                    f'{np.mean(100 * y):.2f} -> {self.feature_names_[col]} -> {np.mean(100 * y_left):.2f} ({y_left.size}) {np.mean(100 * y_right):.2f} ({y_right.size})')

            # save info
            par_node = [{
                'col': self.feature_names_[col],
                'index_col': col,
                'cutoff': cutoff,
                'val': np.mean(y),  # values before splitting
                'flip': flip,
                'val_right': np.mean(y_right),
                'num_pts': y.size,
                'num_pts_right': y_right.size
            }]

            # generate tree for the non-leaf data
            par_node = par_node + self.fit(x_left, y_left, depth + 1, feature_names=feature_names, verbose=verbose)

            self.depth += 1  # increase the depth since we call fit once
            self.rules_ = par_node
            self.complexity_ = len(self.rules_)
            self.classes_ = unique_labels(y)
            return par_node

    def predict_proba(self, X):
        check_is_fitted(self)
        X = check_array(X)
        n = X.shape[0]
        probs = np.zeros(n)
        for i in range(n):
            x = X[i]
            for j, rule in enumerate(self.rules_):
                if j == len(self.rules_) - 1:
                    probs[i] = rule['val']
                elif x[rule['index_col']] >= rule['cutoff']:
                    probs[i] = rule['val_right']
                    break
        return np.vstack((1 - probs, probs)).transpose()  # probs (n, 2)

    def predict(self, X):
        check_is_fitted(self)
        X = check_array(X)
        return np.argmax(self.predict_proba(X), axis=1)

    def __str__(self):
        s = ''
        for rule in self.rules_:
            s += f"mean {rule['val'].round(3)} ({rule['num_pts']} pts)\n"
            if 'col' in rule:
                s += f"if {rule['col']} >= {rule['cutoff']} then {rule['val_right'].round(3)} ({rule['num_pts_right']} pts)\n"
        return s

    def _print_list(self):
        '''Print out the list in a nice way
        '''
        s = ''

        def red(s):
            return f"\033[91m{s}\033[00m"

        def cyan(s):
            return f"\033[96m{s}\033[00m"

        def rule_name(rule):
            if rule['flip']:
                return '~' + rule['col']
            return rule['col']

        # rule = self.rules_[0]
        #     s += f"{red((100 * rule['val']).round(3))}% IwI ({rule['num_pts']} pts)\n"
        for rule in self.rules_:
            s += f"\t{'':>35} => {cyan((100 * rule['val']).round(2)):>6}% risk ({rule['num_pts']} pts)\n"
            #         s += f"\t{'Else':>45} => {cyan((100 * rule['val']).round(2)):>6}% IwI ({rule['val'] * rule['num_pts']:.0f}/{rule['num_pts']} pts)\n"
            if 'col' in rule:
                #             prefix = f"if {rule['col']} >= {rule['cutoff']}"
                prefix = f"if {rule_name(rule)}"
                val = f"{100 * rule['val_right'].round(3):.4}"
                s += f"{prefix:>43} ===> {red(val)}% risk ({rule['num_pts_right']} pts)\n"
        # rule = self.rules_[-1]
        #     s += f"{red((100 * rule['val']).round(3))}% IwI ({rule['num_pts']} pts)\n"
        print(s)

    def _all_same(self, items):
        return all(x == items[0] for x in items)

    def _find_best_split(self, x, y):
        """
        Find the best split from all features
        returns: the column to split on, the cutoff value, and the actual criterion_value
        """
        col = None
        min_criterion_val = 1e10
        cutoff = None

        # iterating through each feature
        for i, c in enumerate(x.T):

            # find the best split of that feature
            criterion_val, cur_cutoff = self._split_on_feature(c, y)

            # found perfect cutoff
            if criterion_val == 0:
                return i, cur_cutoff, criterion_val

            # check if it's best so far
            elif criterion_val <= min_criterion_val:
                min_criterion_val = criterion_val
                col = i
                cutoff = cur_cutoff
        return col, cutoff, min_criterion_val

    def _split_on_feature(self, col, y):
        """
        col: the column we split on
        y: target var
        """
        min_criterion_val = 1e10
        cutoff = 0.5

        # iterate through each value in the column
        for value in np.unique(col):
            # separate y into 2 groups
            y_predict = col < value

            # get criterion val of this split
            criterion_val = self._weighted_criterion(y_predict, y)

            # check if it's the smallest one so far
            if criterion_val <= min_criterion_val:
                min_criterion_val = criterion_val
                cutoff = value
        return min_criterion_val, cutoff

    def _weighted_criterion(self, split_decision, y_real):
        """Returns criterion calculated over a split
        split decision, True/False, and y_true can be multi class
        """
        if split_decision.shape[0] != y_real.shape[0]:
            print('They have to be the same length')
            return None

        # choose the splitting criterion
        if self.criterion == 'entropy':
            criterion_func = self._entropy_criterion
        elif self.criterion == 'gini':
            criterion_func = self._gini_criterion
        elif self.criterion == 'neg_corr':
            return self._neg_corr_criterion(split_decision, y_real)

        # left-hand side criterion
        s_left = criterion_func(y_real[split_decision])

        # right-hand side criterion
        s_right = criterion_func(y_real[~split_decision])

        # overall criterion, again weighted average
        n = y_real.shape[0]
        if self.class_weight is not None:
            sample_weights = np.ones(n)
            for c in self.class_weight.keys():
                idxs_c = y_real == c
                sample_weights[idxs_c] = self.class_weight[c]
            total_weight = np.sum(sample_weights)
            weight_left = np.sum(sample_weights[split_decision]) / total_weight
            # weight_right = np.sum(sample_weights[~split_decision]) / total_weight
        else:
            tot_left_samples = np.sum(split_decision == 1)
            weight_left = tot_left_samples / n

        s = weight_left * s_left + (1 - weight_left) * s_right
        return s

    def _gini_criterion(self, y):
        '''Returns gini index for one node
        = sum(pc * (1 – pc))
        '''
        s = 0
        n = y.shape[0]
        classes = np.unique(y)

        # for each class, get entropy
        for c in classes:
            # weights for each class
            n_c = np.sum(y == c)
            p_c = n_c / n

            # weighted avg
            s += p_c * (1 - p_c)

        return s

    def _entropy_criterion(self, y):
        """Returns entropy of a divided group of data
        Data may have multiple classes
        """
        s = 0
        n = len(y)
        classes = set(y)

        # for each class, get entropy
        for c in classes:
            # weights for each class
            weight = sum(y == c) / n

            def _entropy_from_counts(c1, c2):
                """Returns entropy of a group of data
                c1: count of one class
                c2: count of another class
                """
                if c1 == 0 or c2 == 0:  # when there is only one class in the group, entropy is 0
                    return 0

                def _entropy_func(p): return -p * math.log(p, 2)

                p1 = c1 * 1.0 / (c1 + c2)
                p2 = c2 * 1.0 / (c1 + c2)
                return _entropy_func(p1) + _entropy_func(p2)

            # weighted avg
            s += weight * _entropy_from_counts(sum(y == c), sum(y != c))
        return s

    def _neg_corr_criterion(self, split_decision, y):
        '''Returns negative correlation between y
        and the binary splitting variable split_decision
        y must be binary
        '''
        if np.unique(y).size < 2:
            return 0
        elif np.unique(y).size != 2:
            print('y must be binary output for corr criterion')

        # y should be 1 more often on the "right side" of the split
        if y.sum() < y.size / 2:
            y = 1 - y

        return -1 * np.corrcoef(split_decision.astype(np.int), y)[0, 1]

Ancestors

  • sklearn.base.BaseEstimator
  • RuleList
  • sklearn.base.ClassifierMixin

Subclasses

Methods

def fit(self, X, y, depth: int = 0, feature_names=None, verbose=False)

Params

X: array_like Feature set y: array_like target variable depth the depth of the current layer (used to recurse)

Expand source code
def fit(self, X, y, depth: int = 0, feature_names=None, verbose=False):
    """
    Params
    ------
    X: array_like
        Feature set
    y: array_like
        target variable
    depth
        the depth of the current layer (used to recurse)
    """

    # set self.feature_names and make sure X, y are not pandas type
    if 'pandas' in str(type(X)):
        X = X.values
    else:
        if feature_names is None:
            self.feature_names_ = ['feat ' + str(i) for i in range(X.shape[1])]
    if feature_names is not None:
        self.feature_names_ = feature_names

    # base case 1: no data in this group
    if len(y) == 0:
        return []

    # base case 2: all y is the same in this group
    elif self._all_same(y):
        return [{'val': y[0], 'num_pts': y.size}]

    # base case 3: max depth reached 
    elif depth >= self.max_depth:
        return []

    # recursively generate rule list 
    else:

        # find a split with the best value for the criterion
        col, cutoff, criterion_val = self._find_best_split(X, y)

        # put higher probability of class 1 on the right-hand side
        if self.strategy == 'max':
            y_left = y[X[:, col] < cutoff]  # left-hand side data
            y_right = y[X[:, col] >= cutoff]  # right-hand side data
            if len(y_left) > 0 and np.mean(y_left) > np.mean(y_right):
                flip = True
                tmp = deepcopy(y_left)
                y_left = deepcopy(y_right)
                y_right = tmp
                x_left = X[X[:, col] >= cutoff]
            else:
                flip = False
                x_left = X[X[:, col] < cutoff]
        else:
            print('strategy must be max!')

        # print
        if verbose:
            print(
                f'{np.mean(100 * y):.2f} -> {self.feature_names_[col]} -> {np.mean(100 * y_left):.2f} ({y_left.size}) {np.mean(100 * y_right):.2f} ({y_right.size})')

        # save info
        par_node = [{
            'col': self.feature_names_[col],
            'index_col': col,
            'cutoff': cutoff,
            'val': np.mean(y),  # values before splitting
            'flip': flip,
            'val_right': np.mean(y_right),
            'num_pts': y.size,
            'num_pts_right': y_right.size
        }]

        # generate tree for the non-leaf data
        par_node = par_node + self.fit(x_left, y_left, depth + 1, feature_names=feature_names, verbose=verbose)

        self.depth += 1  # increase the depth since we call fit once
        self.rules_ = par_node
        self.complexity_ = len(self.rules_)
        self.classes_ = unique_labels(y)
        return par_node
def predict(self, X)
Expand source code
def predict(self, X):
    check_is_fitted(self)
    X = check_array(X)
    return np.argmax(self.predict_proba(X), axis=1)
def predict_proba(self, X)
Expand source code
def predict_proba(self, X):
    check_is_fitted(self)
    X = check_array(X)
    n = X.shape[0]
    probs = np.zeros(n)
    for i in range(n):
        x = X[i]
        for j, rule in enumerate(self.rules_):
            if j == len(self.rules_) - 1:
                probs[i] = rule['val']
            elif x[rule['index_col']] >= rule['cutoff']:
                probs[i] = rule['val_right']
                break
    return np.vstack((1 - probs, probs)).transpose()  # probs (n, 2)