Source code for category_encoders.one_hot

"""One-hot or dummy coding"""
import numpy as np
import pandas as pd
import warnings
from category_encoders.ordinal import OrdinalEncoder
import category_encoders.utils as util

__author__ = 'willmcginnis'

[docs]class OneHotEncoder(util.BaseEncoder, util.UnsupervisedTransformerMixin): """Onehot (or dummy) coding for categorical features, produces one feature per category, each binary. Parameters ---------- verbose: int integer indicating verbosity of the output. 0 for none. cols: list a list of columns to encode, if None, all string columns will be encoded. drop_invariant: bool boolean for whether or not to drop columns with 0 variance. return_df: bool boolean for whether to return a pandas DataFrame from transform (otherwise it will be a numpy array). use_cat_names: bool if True, category values will be included in the encoded column names. Since this can result in duplicate column names, duplicates are suffixed with '#' symbol until a unique name is generated. If False, category indices will be used instead of the category values. handle_unknown: str options are 'error', 'return_nan', 'value', and 'indicator'. The default is 'value'. 'error' will raise a `ValueError` at transform time if there are new categories. 'return_nan' will encode a new value as `np.nan` in every dummy column. 'value' will encode a new value as 0 in every dummy column. 'indicator' will add an additional dummy column (in both training and test data). handle_missing: str options are 'error', 'return_nan', 'value', and 'indicator'. The default is 'value'. 'error' will raise a `ValueError` if missings are encountered. 'return_nan' will encode a missing value as `np.nan` in every dummy column. 'value' will encode a missing value as 0 in every dummy column. 'indicator' will treat missingness as its own category, adding an additional dummy column (whether there are missing values in the training set or not). 'ignore' will encode missing values as 0 in every dummy column, NOT adding an additional category. Example ------- >>> from category_encoders import * >>> import pandas as pd >>> from sklearn.datasets import fetch_openml >>> bunch = fetch_openml(name="house_prices", as_frame=True) >>> display_cols = ["Id", "MSSubClass", "MSZoning", "LotFrontage", "YearBuilt", "Heating", "CentralAir"] >>> y = >>> X = pd.DataFrame(, columns=bunch.feature_names)[display_cols] >>> enc = OneHotEncoder(cols=['CentralAir', 'Heating'], handle_unknown='indicator').fit(X, y) >>> numeric_dataset = enc.transform(X) >>> print( <class 'pandas.core.frame.DataFrame'> RangeIndex: 1460 entries, 0 to 1459 Data columns (total 15 columns): # Column Non-Null Count Dtype --- ------ -------------- ----- 0 Id 1460 non-null float64 1 MSSubClass 1460 non-null float64 2 MSZoning 1460 non-null object 3 LotFrontage 1201 non-null float64 4 YearBuilt 1460 non-null float64 5 Heating_1 1460 non-null int64 6 Heating_2 1460 non-null int64 7 Heating_3 1460 non-null int64 8 Heating_4 1460 non-null int64 9 Heating_5 1460 non-null int64 10 Heating_6 1460 non-null int64 11 Heating_-1 1460 non-null int64 12 CentralAir_1 1460 non-null int64 13 CentralAir_2 1460 non-null int64 14 CentralAir_-1 1460 non-null int64 dtypes: float64(4), int64(10), object(1) memory usage: 171.2+ KB None References ---------- .. [1] Contrast Coding Systems for Categorical Variables, from .. [2] Gregory Carey (2003). Coding Categorical Variables, from """ prefit_ordinal = True encoding_relation = util.EncodingRelation.ONE_TO_N_UNIQUE def __init__(self, verbose=0, cols=None, drop_invariant=False, return_df=True, handle_missing='value', handle_unknown='value', use_cat_names=False): super().__init__(verbose=verbose, cols=cols, drop_invariant=drop_invariant, return_df=return_df, handle_unknown=handle_unknown, handle_missing=handle_missing) self.mapping = None self.ordinal_encoder = None self.use_cat_names = use_cat_names @property def category_mapping(self): return self.mapping def _fit(self, X, y=None, **kwargs): oe_missing_strat = { 'error': 'error', 'return_nan': 'return_nan', 'value': 'value', 'indicator': 'return_nan', 'ignore': 'return_nan' }[self.handle_missing] self.ordinal_encoder = OrdinalEncoder( verbose=self.verbose, cols=self.cols, handle_unknown='value', handle_missing=oe_missing_strat, ) self.ordinal_encoder = self.mapping = self.generate_mapping() def generate_mapping(self): mapping = [] found_column_counts = {} for switch in self.ordinal_encoder.mapping: col = switch.get('col') values = switch.get('mapping').copy(deep=True) if self.handle_missing == 'value': values = values[values > 0] if len(values) == 0: continue index = [] new_columns = [] append_nan_to_index = False for cat_name, class_ in values.items(): if pd.isna(cat_name) and self.handle_missing in ['return_nan', 'ignore']: # we don't want a mapping column if return_nan # but do add the index to the end append_nan_to_index = class_ continue if self.use_cat_names: n_col_name = f"{col}_{cat_name}" found_count = found_column_counts.get(n_col_name, 0) found_column_counts[n_col_name] = found_count + 1 n_col_name += '#' * found_count else: n_col_name = f"{col}_{class_}" index.append(class_) new_columns.append(n_col_name) if self.handle_unknown == 'indicator': n_col_name = f"{col}_-1" if self.use_cat_names: found_count = found_column_counts.get(n_col_name, 0) found_column_counts[n_col_name] = found_count + 1 n_col_name += '#' * found_count new_columns.append(n_col_name) index.append(-1) if append_nan_to_index: index.append(append_nan_to_index) base_matrix = np.eye(N=len(index), M=len(new_columns), dtype=int) base_df = pd.DataFrame(data=base_matrix, columns=new_columns, index=index) if self.handle_unknown == 'value': base_df.loc[-1] = 0 elif self.handle_unknown == 'return_nan': base_df.loc[-1] = np.nan if self.handle_missing == 'return_nan': base_df.loc[-2] = np.nan elif self.handle_missing in ['value','ignore']: base_df.loc[-2] = 0 mapping.append({'col': col, 'mapping': base_df}) return mapping def _transform(self, X): X = self.ordinal_encoder.transform(X) if self.handle_unknown == 'error': if X[self.cols].isin([-1]).any().any(): raise ValueError('Columns to be encoded can not contain new values') X = self.get_dummies(X) return X
[docs] def inverse_transform(self, X_in): """ Perform the inverse transformation to encoded data. Parameters ---------- X_in : array-like, shape = [n_samples, n_features] Returns ------- p: array, the same size of X_in """ # fail fast if self._dim is None: raise ValueError('Must train encoder before it can be used to inverse_transform data') # first check the type and make deep copy X = util.convert_input(X_in, columns=self.feature_names_out_, deep=True) X = self.reverse_dummies(X, self.mapping) # then make sure that it is the right size if X.shape[1] != self._dim: if self.drop_invariant: raise ValueError(f"Unexpected input dimension {X.shape[1]}, the attribute drop_invariant should " "be False when transforming the data") else: raise ValueError(f'Unexpected input dimension {X.shape[1]}, expected {self._dim}') if not list(self.cols): return X if self.return_df else X.values for switch in self.ordinal_encoder.mapping: column_mapping = switch.get('mapping') inverse = pd.Series(data=column_mapping.index, index=column_mapping.values) X[switch.get('col')] = X[switch.get('col')].map(inverse).astype(switch.get('data_type')) if self.handle_unknown == 'return_nan' and self.handle_missing == 'return_nan': for col in self.cols: if X[switch.get('col')].isnull().any(): warnings.warn("inverse_transform is not supported because transform impute " f"the unknown category nan when encode {col}") return X if self.return_df else X.values
[docs] def get_dummies(self, X_in): """ Convert numerical variable into dummy variables Parameters ---------- X_in: DataFrame Returns ------- dummies : DataFrame """ X = X_in.copy(deep=True) cols = X.columns.values.tolist() for switch in self.mapping: col = switch.get('col') mod = switch.get('mapping') base_df = mod.reindex(X[col].fillna(-2)) base_df = base_df.set_index(X.index) X = pd.concat([base_df, X], axis=1) old_column_index = cols.index(col) cols[old_column_index: old_column_index + 1] = mod.columns X = X.reindex(columns=cols) return X
[docs] def reverse_dummies(self, X, mapping): """ Convert dummy variable into numerical variables Parameters ---------- X : DataFrame mapping: list-like Contains mappings of column to be transformed to it's new columns and value represented Returns ------- numerical: DataFrame """ out_cols = X.columns.values.tolist() mapped_columns = [] for switch in mapping: col = switch.get('col') mod = switch.get('mapping') insert_at = out_cols.index(mod.columns[0]) X.insert(insert_at, col, 0) positive_indexes = mod.index[mod.index > 0] for i in range(positive_indexes.shape[0]): existing_col = mod.columns[i] val = positive_indexes[i] X.loc[X[existing_col] == 1, col] = val mapped_columns.append(existing_col) X.drop(mod.columns, axis=1, inplace=True) out_cols = X.columns.values.tolist() return X