Source code for ibmdbpy.feature_selection.gain_ratio

# -*- coding: utf-8 -*-
Created on Mon Nov 23 09:48:18 2015

@author: efouche
from __future__ import division
from __future__ import unicode_literals
from __future__ import print_function
from __future__ import absolute_import
from builtins import dict
from future import standard_library

from collections import OrderedDict

from ibmdbpy.feature_selection.entropy import entropy 

from ibmdbpy.internals import idadf_state
from ibmdbpy.utils import timed

import numpy as np 
import pandas as pd

from ibmdbpy.feature_selection.private import _check_input

[docs]def gain_ratio(idadf, target = None, features = None, symmetry=True, ignore_indexer=True): """ Compute the gain ratio coefficients between a set of features and a set of target in an IdaDataFrame. Parameters ---------- idadf : IdaDataFrame target : str or list of str, optional A column or list of columns against to be used as target. Per default, consider all columns features : str or list of str, optional A column or list of columns to be used as features. Per default, consider all columns. symmetry : bool, default: True If True, compute the symmetric gain ratio as defined by [Lopez de Mantaras 1991]. Otherwise, the asymmetric gain ratio. ignore_indexer : bool, default: True Per default, ignore the column declared as indexer in idadf Returns ------- Pandas.DataFrame or Pandas.Series if only one target Notes ----- Input columns as target and features should be categorical, otherwise this measure does not make much sense. Examples -------- >>> idadf = IdaDataFrame(idadb, "IRIS") >>> gain_ratio(idadf) """ # Check input target, features = _check_input(idadf, target, features, ignore_indexer) entropy_dict = dict() length = len(idadf) values = OrderedDict() corrector = length*np.log(length) for t in target: if t not in values: values[t] = OrderedDict() features_notarget = [x for x in features if (x != t)] for feature in features_notarget: if feature not in values: values[feature] = OrderedDict() if t not in values[feature]: # i.e. it was not already computed if t not in entropy_dict: entropy_dict[t] = entropy(idadf, t, mode = "raw") if feature not in entropy_dict: entropy_dict[feature] = entropy(idadf, feature, mode = "raw") join_entropy = entropy(idadf, [t] + [feature], mode = "raw") disjoin_entropy = entropy_dict[t] + entropy_dict[feature] info_gain = (disjoin_entropy - join_entropy) if symmetry: gain_ratio = (info_gain + corrector)/(disjoin_entropy + 2*corrector) # 2* because symmetric values[t][feature] = gain_ratio if feature in target: values[feature][t] = gain_ratio else: gain_ratio_1 = (info_gain + corrector)/(entropy_dict[t] + corrector) values[t][feature] = gain_ratio_1 if feature in target: gain_ratio_2 = (info_gain + corrector)/(entropy_dict[feature] + corrector) values[feature][t] = gain_ratio_2 ### Fill the matrix result = pd.DataFrame(values).fillna(np.nan) result = result.dropna(axis=1, how="all") if len(result.columns) > 1: order = [x for x in result.columns if x in features] + [x for x in features if x not in result.columns] result = result.reindex(order) if len(result.columns) == 1: if len(result) == 1: result = result.iloc[0,0] else: result = result[result.columns[0]].copy() result.sort(ascending = True) else: result = result.fillna(1) return result