class sklearn.preprocessing.FunctionTransformer(func=None, validate=True, accept_sparse=False, pass_y=False)[source]

Constructs a transformer from an arbitrary callable.

A FunctionTransformer forwards its X (and optionally y) arguments to a user-defined function or function object and returns the result of this function. This is useful for stateless transformations such as taking the log of frequencies, doing custom scaling, etc.

A FunctionTransformer will not do any checks on its function’s output.

Note: If a lambda is used as the function, then the resulting transformer will not be pickleable.

New in version 0.17.


func : callable, optional default=None

The callable to use for the transformation. This will be passed the same arguments as transform, with args and kwargs forwarded. If func is None, then func will be the identity function.

validate : bool, optional default=True

Indicate that the input X array should be checked before calling func. If validate is false, there will be no input validation. If it is true, then X will be converted to a 2-dimensional NumPy array or sparse matrix. If this conversion is not possible or X contains NaN or infinity, an exception is raised.

accept_sparse : boolean, optional

Indicate that func accepts a sparse matrix as input. If validate is False, this has no effect. Otherwise, if accept_sparse is false, sparse matrix inputs will cause an exception to be raised.

pass_y: bool, optional default=False :

Indicate that transform should forward the y argument to the inner callable.


fit(X[, y])
fit_transform(X[, y]) Fit to data, then transform it.
get_params([deep]) Get parameters for this estimator.
set_params(**params) Set the parameters of this estimator.
transform(X[, y])
__init__(func=None, validate=True, accept_sparse=False, pass_y=False)[source]
fit_transform(X, y=None, **fit_params)[source]

Fit to data, then transform it.

Fits transformer to X and y with optional parameters fit_params and returns a transformed version of X.


X : numpy array of shape [n_samples, n_features]

Training set.

y : numpy array of shape [n_samples]

Target values.


X_new : numpy array of shape [n_samples, n_features_new]

Transformed array.


Get parameters for this estimator.


deep: boolean, optional :

If True, will return the parameters for this estimator and contained subobjects that are estimators.


params : mapping of string to any

Parameter names mapped to their values.


Set the parameters of this estimator.

The method works on simple estimators as well as on nested objects (such as pipelines). The former have parameters of the form <component>__<parameter> so that it’s possible to update each component of a nested object.

Returns:self :

Examples using sklearn.preprocessing.FunctionTransformer