Imputation for completing missing values using k-Nearest Neighbors.
Each sample's missing values are imputed using the mean value from `n_neighbors` nearest neighbors found in the training set. Two samples are close if the features that neither is missing are close.
Read more in the :ref:`User Guide <knnimpute>`.
.. versionadded:: 0.22
Parameters ---------- missing_values : number, string, np.nan or None, default=`np.nan` The placeholder for the missing values. All occurrences of `missing_values` will be imputed.
n_neighbors : int, default=5 Number of neighboring samples to use for imputation.
weights : 'uniform', 'distance'
or callable, default='uniform' Weight function used in prediction. Possible values:
- 'uniform' : uniform weights. All points in each neighborhood are weighted equally.
- 'distance' : weight points by the inverse of their distance. in this case, closer neighbors of a query point will have a greater influence than neighbors which are further away.
- callable : a user-defined function which accepts an array of distances, and returns an array of the same shape containing the weights.
metric : 'nan_euclidean'
or callable, default='nan_euclidean' Distance metric for searching neighbors. Possible values:
- 'nan_euclidean'
- callable : a user-defined function which conforms to the definition of ``_pairwise_callable(X, Y, metric, **kwds)``. The function accepts two arrays, X and Y, and a `missing_values` keyword in `kwds` and returns a scalar distance value.
copy : bool, default=True If True, a copy of X will be created. If False, imputation will be done in-place whenever possible.
add_indicator : bool, default=False If True, a :class:`MissingIndicator` transform will stack onto the output of the imputer's transform. This allows a predictive estimator to account for missingness despite imputation. If a feature has no missing values at fit/train time, the feature won't appear on the missing indicator even if there are missing values at transform/test time.
Attributes ---------- indicator_ : :class:`sklearn.impute.MissingIndicator` Indicator used to add binary indicators for missing values. ``None`` if add_indicator is False.
References ---------- * Olga Troyanskaya, Michael Cantor, Gavin Sherlock, Pat Brown, Trevor Hastie, Robert Tibshirani, David Botstein and Russ B. Altman, Missing value estimation methods for DNA microarrays, BIOINFORMATICS Vol. 17 no. 6, 2001 Pages 520-525.
Examples -------- >>> import numpy as np >>> from sklearn.impute import KNNImputer >>> X = [1, 2, np.nan], [3, 4, 3], [np.nan, 6, 5], [8, 8, 7]
>>> imputer = KNNImputer(n_neighbors=2) >>> imputer.fit_transform(X) array([1. , 2. , 4. ],
[3. , 4. , 3. ],
[5.5, 6. , 5. ],
[8. , 8. , 7. ]
)