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# `sklearn.preprocessing`.SplineTransformer

class sklearn.preprocessing.SplineTransformer(n_knots=5, degree=3, *, knots='uniform', extrapolation='constant', include_bias=True, order='C', sparse_output=False)

  Generate univariate B-spline bases for features.

  Generate a new feature matrix consisting of `n_splines=n_knots + degree - 1` (`n_knots - 1` for `extrapolation="periodic"`) spline basis functions (B-splines) of polynomial order=`degree` for each feature.

  Read more in the User Guide.

  New in version 1.0.

  Parameters:
    n_knots int, default=5

      Number of knots of the splines if `knots` equals one of {‘uniform’, ‘quantile’}. Must be larger or equal 2. Ignored if `knots` is array-like.

    degree int, default=3

      The polynomial degree of the spline basis. Must be a non-negative integer.

    knots{‘uniform’, ‘quantile’} or array-like of shape (n_knots, n_features), default=’uniform’

      Set knot positions such that first knot <= features <= last knot.

      - If ‘uniform’, `n_knots` number of knots are distributed uniformly from min to max values of the features.

      - If ‘quantile’, they are distributed uniformly along the quantiles of the features.

      - If an array-like is given, it directly specifies the sorted knot positions including the boundary knots. Note that, internally, `degree` number of knots are added before the first knot, the same after the last knot.

    extrapolation{‘error’, ‘constant’, ‘linear’, ‘continue’, ‘periodic’}, default=’constant’

      If ‘error’, values outside the min and max values of the training features raises a `ValueError`. If ‘constant’, the value of the splines at minimum and maximum value of the features is used as constant extrapolation. If ‘linear’, a linear extrapolation is used. If ‘continue’, the splines are extrapolated as is, i.e. option `extrapolate=True` in `scipy.interpolate.BSpline`. If ‘periodic’, periodic splines with a periodicity equal to the distance between the first and last knot are used. Periodic splines enforce equal function values and derivatives at the first and last knot. For example, this makes it possible to avoid introducing an arbitrary jump between Dec 31st and Jan 1st in spline features derived from a naturally periodic “day-of-year” input feature. In this case it is recommended to manually set the knot values to control the period.

    include_bias bool, default=True

      If False, then the last spline element inside the data range of a feature is dropped. As B-splines sum to one over the spline basis functions for each data point, they implicitly include a bias term, i.e. a column of ones. It acts as an intercept term in a linear models.

    order{‘C’, ‘F’}, default=’C’

      Order of output array in the dense case. `'F'` order is faster to compute, but may slow down subsequent estimators.

    sparse_output bool, default=False

      Will return sparse CSR matrix if set True else will return an array. This option is only available with `scipy>=1.8`.

      New in version 1.2.

  Attributes:
    bsplines_list of shape (n_features,)

      List of BSplines objects, one for each feature.

    n_features_in_int

      The total number of input features.

    feature_names_in_ndarray of shape (`n_features_in_`,)

      Names of features seen during fit. Defined only when `X` has feature names that are all strings.

      New in version 1.0.

    n_features_out_int

      The total number of output features, which is computed as `n_features * n_splines`, where `n_splines` is the number of bases elements of the B-splines, `n_knots + degree - 1` for non-periodic splines and `n_knots - 1` for periodic ones. If `include_bias=False`, then it is only `n_features * (n_splines - 1)`.

  See also

  `KBinsDiscretizer`

    Transformer that bins continuous data into intervals.

  `PolynomialFeatures`

    Transformer that generates polynomial and interaction features.

  Notes

  High degrees and a high number of knots can cause overfitting.

  See examples/linear_model/plot_polynomial_interpolation.py.

  Examples

      >>> import numpy as np
      >>> from sklearn.preprocessing import SplineTransformer
      >>> X = np.arange(6).reshape(6, 1)
      >>> spline = SplineTransformer(degree=2, n_knots=3)
      >>> spline.fit_transform(X)
      array([[0.5 , 0.5 , 0.  , 0.  ],
             [0.18, 0.74, 0.08, 0.  ],
             [0.02, 0.66, 0.32, 0.  ],
             [0.  , 0.32, 0.66, 0.02],
             [0.  , 0.08, 0.74, 0.18],
             [0.  , 0.  , 0.5 , 0.5 ]])

  Methods

  `fit`(X[, y, sample_weight]) | Compute knot positions of splines.
  `fit_transform`(X[, y]) | Fit to data, then transform it.
  `get_feature_names_out`([input_features]) | Get output feature names for transformation.
  `get_metadata_routing`() | Get metadata routing of this object.
  `get_params`([deep]) | Get parameters for this estimator.
  `set_fit_request`(*[, sample_weight]) | Request metadata passed to the `fit` method.
  `set_output`(*[, transform]) | Set output container.
  `set_params`(**params) | Set the parameters of this estimator.
  `transform`(X) | Transform each feature data to B-splines.

  fit(X, y=None, sample_weight=None)

    Compute knot positions of splines.

    Parameters:
      X array-like of shape (n_samples, n_features)

        The data.

      y None

        Ignored.

      sample_weight array-like of shape (n_samples,), default = None

        Individual weights for each sample. Used to calculate quantiles if `knots="quantile"`. For `knots="uniform"`, zero weighted observations are ignored for finding the min and max of `X`.

    Returns:
      self object

        Fitted transformer.

  fit_transform(X, y=None, **fit_params)

    Fit to data, then transform it.

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

    Parameters:
      X array-like of shape (n_samples, n_features)

        Input samples.

      y array-like of shape (n_samples,) or (n_samples, n_outputs), default=None

        Target values (None for unsupervised transformations).

      **fit_params dict

        Additional fit parameters.

    Returns:
      X_new ndarray array of shape (n_samples, n_features_new)

        Transformed array.

  get_feature_names_out(input_features=None)

    Get output feature names for transformation.

    Parameters:
      input_features array-like of str or None, default=None

        Input features.

        - If `input_features` is `None`, then `feature_names_in_` is used as feature names in. If `feature_names_in_` is not defined, then the following input feature names are generated: `["x0", "x1", ..., "x(n_features_in_ - 1)"]`.

        - If `input_features` is an array-like, then `input_features` must match `feature_names_in_` if `feature_names_in_` is defined.

    Returns:
      feature_names_out ndarray of str objects

        Transformed feature names.

  get_metadata_routing()

    Get metadata routing of this object.

    Please check User Guide on how the routing mechanism works.

    Returns:
      routing MetadataRequest

        A `MetadataRequest` encapsulating routing information.

  get_params(deep=True)

    Get parameters for this estimator.

    Parameters:
      deep bool, default=True

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

    Returns:
      params dict

        Parameter names mapped to their values.

  set_fit_request(*, sample_weight: bool | None | str = '$UNCHANGED$') → SplineTransformer

    Request metadata passed to the `fit` method.

    Note that this method is only relevant if `enable_metadata_routing=True` (see `sklearn.set_config`). Please see User Guide on how the routing mechanism works.

    The options for each parameter are:

    - `True`: metadata is requested, and passed to `fit` if provided. The request is ignored if metadata is not provided.

    - `False`: metadata is not requested and the meta-estimator will not pass it to `fit`.

    - `None`: metadata is not requested, and the meta-estimator will raise an error if the user provides it.

    - `str`: metadata should be passed to the meta-estimator with this given alias instead of the original name.

    The default (`sklearn.utils.metadata_routing.UNCHANGED`) retains the existing request. This allows you to change the request for some parameters and not others.

    New in version 1.3.

    Note

    This method is only relevant if this estimator is used as a sub-estimator of a meta-estimator, e.g. used inside a `Pipeline`. Otherwise it has no effect.

    Parameters:
      sample_weight str, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED

        Metadata routing for `sample_weight` parameter in `fit`.

    Returns:
      self object

        The updated object.

  set_output(*, transform=None)

    Set output container.

    See Introducing the set_output API for an example on how to use the API.

    Parameters:
      transform{“default”, “pandas”}, default=None

        Configure output of `transform` and `fit_transform`.

        - `"default"`: Default output format of a transformer

        - `"pandas"`: DataFrame output

        - `None`: Transform configuration is unchanged

    Returns:
      self estimator instance

        Estimator instance.

  set_params(**params)

    Set the parameters of this estimator.

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

    Parameters:
      **params dict

        Estimator parameters.

    Returns:
      self estimator instance

        Estimator instance.

  transform(X)

    Transform each feature data to B-splines.

    Parameters:
      X array-like of shape (n_samples, n_features)

        The data to transform.

    Returns:
      XBS{ndarray, sparse matrix} of shape (n_samples, n_features * n_splines)

        The matrix of features, where n_splines is the number of bases elements of the B-splines, n_knots + degree - 1.

## Examples using `sklearn.preprocessing.SplineTransformer`

Release Highlights for scikit-learn 1.0

Release Highlights for scikit-learn 1.0

Time-related feature engineering

Time-related feature engineering

Polynomial and Spline interpolation

Polynomial and Spline interpolation

Evaluation of outlier detection estimators

Evaluation of outlier detection estimators