import numpy as np import pandas as pd from sklearn.preprocessing import OneHotEncoder as SKOneHotEncoder from .encoder import CategoricalEncoder [docs]class OneHotEncoder(CategoricalEncoder): """One-hot encoder to encode non-numeric data.""" name = 'One Hot Encoder' hyperparameter_ranges = {} [docs] def __init__(self, top_n=10, categories=None, drop=None, handle_unknown="ignore", handle_missing="error", random_state=0, **kwargs): """Initalizes an transformer that encodes categorical features in a one-hot numeric array." Arguments: top_n (int): Number of categories per column to encode. If None, all categories will be encoded. Otherwise, the `n` most frequent will be encoded and all others will be dropped. Defaults to 10. categories (list): A two dimensional list of categories, where `categories[i]` is a list of the categories for the column at index `i`. This can also be `None`, or `"auto"` if `top_n` is not None. Defaults to None. drop (string): Method ("first" or "if_binary") to use to drop one category per feature. Can also be a list specifying which method to use for each feature. Defaults to None. handle_unknown (string): Whether to ignore or error for unknown categories for a feature encountered during `fit` or `transform`. If either `top_n` or `categories` is used to limit the number of categories per column, this must be "ignore". Defaults to "ignore". handle_missing (string): Options for how to handle missing (NaN) values encountered during `fit` or `transform`. If this is set to "as_category" and NaN values are within the `n` most frequent, "nan" values will be encoded as their own column. If this is set to "error", any missing values encountered will raise an error. Defaults to "error". """ parameters = {"top_n": top_n, "categories": categories, "drop": drop, "handle_unknown": handle_unknown, "handle_missing": handle_missing} parameters.update(kwargs) # Check correct inputs unknown_input_options = ["ignore", "error"] missing_input_options = ["as_category", "error"] if handle_unknown not in unknown_input_options: raise ValueError("Invalid input {} for handle_unknown".format(handle_unknown)) if handle_missing not in missing_input_options: raise ValueError("Invalid input {} for handle_missing".format(handle_missing)) if top_n is not None and categories is not None: raise ValueError("Cannot use categories and top_n arguments simultaneously") self._encoder = None super().__init__(parameters=parameters, component_obj=None, random_state=random_state) def _get_cat_cols(self, X): """Get names of 'object' or 'categorical' columns in the DataFrame.""" obj_cols = [] for idx, dtype in enumerate(X.dtypes): if dtype == np.object or pd.api.types.is_categorical_dtype(dtype): obj_cols.append(X.columns.values[idx]) return obj_cols [docs] def fit(self, X, y=None): top_n = self.parameters['top_n'] if not isinstance(X, pd.DataFrame): X = pd.DataFrame(X) X_t = X cols_to_encode = self._get_cat_cols(X_t) if self.parameters['handle_missing'] == "as_category": X_t[cols_to_encode] = X_t[cols_to_encode].replace(np.nan, "nan") elif self.parameters['handle_missing'] == "error" and X.isnull().any().any(): raise ValueError("Input contains NaN") if len(cols_to_encode) == 0: categories = 'auto' elif self.parameters['categories'] is not None: categories = self.parameters['categories'] if len(categories) != len(cols_to_encode) or not isinstance(categories[0], list): raise ValueError('Categories argument must contain a list of categories for each categorical feature') else: categories = [] for col in X_t[cols_to_encode]: value_counts = X_t[col].value_counts(dropna=False).to_frame() if top_n is None or len(value_counts) <= top_n: unique_values = value_counts.index.tolist() else: value_counts = value_counts.sample(frac=1, random_state=self.random_state) value_counts = value_counts.sort_values([col], ascending=False, kind='mergesort') unique_values = value_counts.head(top_n).index.tolist() unique_values = np.sort(unique_values) categories.append(unique_values) # Create an encoder to pass off the rest of the computation to self._encoder = SKOneHotEncoder(categories=categories, drop=self.parameters['drop'], handle_unknown=self.parameters['handle_unknown']) self._encoder.fit(X_t[cols_to_encode]) return self [docs] def transform(self, X, y=None): """One-hot encode the input DataFrame. Arguments: X (pd.DataFrame): Dataframe of features. y (pd.Series): Ignored. Returns: Transformed dataframe, where each categorical feature has been encoded into numerical columns using one-hot encoding. """ if self._encoder is None: raise RuntimeError("You must fit one hot encoder before calling transform!") if not isinstance(X, pd.DataFrame): X = pd.DataFrame(X) cat_cols = self._get_cat_cols(X) if self.parameters['handle_missing'] == "as_category": X[cat_cols] = X[cat_cols].replace(np.nan, "nan") if self.parameters['handle_missing'] == "error" and X.isnull().any().any(): raise ValueError("Input contains NaN") X_t = pd.DataFrame() # Add the non-categorical columns, untouched for col in X.columns: if col not in cat_cols: X_t = pd.concat([X_t, X[col]], axis=1) # Call sklearn's transform on the categorical columns if len(cat_cols) > 0: X_cat = pd.DataFrame(self._encoder.transform(X[cat_cols]).toarray()) cat_cols_str = [str(c) for c in cat_cols] X_cat.columns = self._encoder.get_feature_names(input_features=cat_cols_str) X_t = pd.concat([X_t.reindex(X_cat.index), X_cat], axis=1) return X_t