176 lines
5.8 KiB
Python
176 lines
5.8 KiB
Python
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import warnings
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from ..base import BaseEstimator, TransformerMixin
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from ..utils.validation import _allclose_dense_sparse
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from ..utils.validation import _deprecate_positional_args
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def _identity(X):
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"""The identity function.
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"""
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return X
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class FunctionTransformer(TransformerMixin, BaseEstimator):
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"""Constructs a transformer from an arbitrary callable.
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A FunctionTransformer forwards its X (and optionally y) arguments to a
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user-defined function or function object and returns the result of this
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function. This is useful for stateless transformations such as taking the
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log of frequencies, doing custom scaling, etc.
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Note: If a lambda is used as the function, then the resulting
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transformer will not be pickleable.
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.. versionadded:: 0.17
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Read more in the :ref:`User Guide <function_transformer>`.
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Parameters
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----------
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func : callable, default=None
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The callable to use for the transformation. This will be passed
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the same arguments as transform, with args and kwargs forwarded.
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If func is None, then func will be the identity function.
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inverse_func : callable, default=None
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The callable to use for the inverse transformation. This will be
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passed the same arguments as inverse transform, with args and
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kwargs forwarded. If inverse_func is None, then inverse_func
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will be the identity function.
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validate : bool, default=False
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Indicate that the input X array should be checked before calling
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``func``. The possibilities are:
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- If False, there is no input validation.
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- If True, then X will be converted to a 2-dimensional NumPy array or
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sparse matrix. If the conversion is not possible an exception is
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raised.
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.. versionchanged:: 0.22
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The default of ``validate`` changed from True to False.
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accept_sparse : bool, default=False
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Indicate that func accepts a sparse matrix as input. If validate is
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False, this has no effect. Otherwise, if accept_sparse is false,
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sparse matrix inputs will cause an exception to be raised.
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check_inverse : bool, default=True
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Whether to check that or ``func`` followed by ``inverse_func`` leads to
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the original inputs. It can be used for a sanity check, raising a
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warning when the condition is not fulfilled.
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.. versionadded:: 0.20
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kw_args : dict, default=None
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Dictionary of additional keyword arguments to pass to func.
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.. versionadded:: 0.18
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inv_kw_args : dict, default=None
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Dictionary of additional keyword arguments to pass to inverse_func.
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.. versionadded:: 0.18
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Examples
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--------
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>>> import numpy as np
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>>> from sklearn.preprocessing import FunctionTransformer
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>>> transformer = FunctionTransformer(np.log1p)
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>>> X = np.array([[0, 1], [2, 3]])
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>>> transformer.transform(X)
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array([[0. , 0.6931...],
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[1.0986..., 1.3862...]])
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"""
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@_deprecate_positional_args
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def __init__(self, func=None, inverse_func=None, *, validate=False,
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accept_sparse=False, check_inverse=True, kw_args=None,
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inv_kw_args=None):
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self.func = func
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self.inverse_func = inverse_func
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self.validate = validate
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self.accept_sparse = accept_sparse
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self.check_inverse = check_inverse
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self.kw_args = kw_args
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self.inv_kw_args = inv_kw_args
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def _check_input(self, X):
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if self.validate:
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return self._validate_data(X, accept_sparse=self.accept_sparse)
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return X
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def _check_inverse_transform(self, X):
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"""Check that func and inverse_func are the inverse."""
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idx_selected = slice(None, None, max(1, X.shape[0] // 100))
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X_round_trip = self.inverse_transform(self.transform(X[idx_selected]))
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if not _allclose_dense_sparse(X[idx_selected], X_round_trip):
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warnings.warn("The provided functions are not strictly"
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" inverse of each other. If you are sure you"
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" want to proceed regardless, set"
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" 'check_inverse=False'.", UserWarning)
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def fit(self, X, y=None):
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"""Fit transformer by checking X.
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If ``validate`` is ``True``, ``X`` will be checked.
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Parameters
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----------
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X : array-like, shape (n_samples, n_features)
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Input array.
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Returns
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-------
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self
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"""
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X = self._check_input(X)
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if (self.check_inverse and not (self.func is None or
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self.inverse_func is None)):
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self._check_inverse_transform(X)
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return self
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def transform(self, X):
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"""Transform X using the forward function.
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Parameters
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----------
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X : array-like, shape (n_samples, n_features)
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Input array.
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Returns
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-------
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X_out : array-like, shape (n_samples, n_features)
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Transformed input.
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"""
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return self._transform(X, func=self.func, kw_args=self.kw_args)
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def inverse_transform(self, X):
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"""Transform X using the inverse function.
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Parameters
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----------
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X : array-like, shape (n_samples, n_features)
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Input array.
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Returns
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-------
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X_out : array-like, shape (n_samples, n_features)
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Transformed input.
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"""
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return self._transform(X, func=self.inverse_func,
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kw_args=self.inv_kw_args)
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def _transform(self, X, func=None, kw_args=None):
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X = self._check_input(X)
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if func is None:
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func = _identity
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return func(X, **(kw_args if kw_args else {}))
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def _more_tags(self):
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return {'no_validation': not self.validate,
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'stateless': True}
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