sklearn.model_selection
.KFold¶
- class sklearn.model_selection.KFold(n_splits=5, *, shuffle=False, random_state=None)[source]¶
K-Folds cross-validator
Provides train/test indices to split data in train/test sets. Split dataset into k consecutive folds (without shuffling by default).
Each fold is then used once as a validation while the k - 1 remaining folds form the training set.
Read more in the User Guide.
- Parameters:
- n_splitsint, default=5
Number of folds. Must be at least 2.
Changed in version 0.22:
n_splits
default value changed from 3 to 5.- shufflebool, default=False
Whether to shuffle the data before splitting into batches. Note that the samples within each split will not be shuffled.
- random_stateint, RandomState instance or None, default=None
When
shuffle
is True,random_state
affects the ordering of the indices, which controls the randomness of each fold. Otherwise, this parameter has no effect. Pass an int for reproducible output across multiple function calls. See Glossary.
See also
StratifiedKFold
Takes class information into account to avoid building folds with imbalanced class distributions (for binary or multiclass classification tasks).
GroupKFold
K-fold iterator variant with non-overlapping groups.
RepeatedKFold
Repeats K-Fold n times.
Notes
The first
n_samples % n_splits
folds have sizen_samples // n_splits + 1
, other folds have sizen_samples // n_splits
, wheren_samples
is the number of samples.Randomized CV splitters may return different results for each call of split. You can make the results identical by setting
random_state
to an integer.Examples
>>> import numpy as np >>> from sklearn.model_selection import KFold >>> X = np.array([[1, 2], [3, 4], [1, 2], [3, 4]]) >>> y = np.array([1, 2, 3, 4]) >>> kf = KFold(n_splits=2) >>> kf.get_n_splits(X) 2 >>> print(kf) KFold(n_splits=2, random_state=None, shuffle=False) >>> for train_index, test_index in kf.split(X): ... print("TRAIN:", train_index, "TEST:", test_index) ... X_train, X_test = X[train_index], X[test_index] ... y_train, y_test = y[train_index], y[test_index] TRAIN: [2 3] TEST: [0 1] TRAIN: [0 1] TEST: [2 3]
Methods
get_n_splits
([X, y, groups])Returns the number of splitting iterations in the cross-validator
split
(X[, y, groups])Generate indices to split data into training and test set.
- get_n_splits(X=None, y=None, groups=None)[source]¶
Returns the number of splitting iterations in the cross-validator
- Parameters:
- Xobject
Always ignored, exists for compatibility.
- yobject
Always ignored, exists for compatibility.
- groupsobject
Always ignored, exists for compatibility.
- Returns:
- n_splitsint
Returns the number of splitting iterations in the cross-validator.
- split(X, y=None, groups=None)[source]¶
Generate indices to split data into training and test set.
- Parameters:
- Xarray-like of shape (n_samples, n_features)
Training data, where
n_samples
is the number of samples andn_features
is the number of features.- yarray-like of shape (n_samples,), default=None
The target variable for supervised learning problems.
- groupsarray-like of shape (n_samples,), default=None
Group labels for the samples used while splitting the dataset into train/test set.
- Yields:
- trainndarray
The training set indices for that split.
- testndarray
The testing set indices for that split.
Examples using sklearn.model_selection.KFold
¶
Feature agglomeration vs. univariate selection
Gradient Boosting Out-of-Bag estimates
Nested versus non-nested cross-validation
Visualizing cross-validation behavior in scikit-learn
Cross-validation on diabetes Dataset Exercise