sklearn.tree
.ExtraTreeClassifier¶

class
sklearn.tree.
ExtraTreeClassifier
(*, criterion='gini', splitter='random', max_depth=None, min_samples_split=2, min_samples_leaf=1, min_weight_fraction_leaf=0.0, max_features='auto', random_state=None, max_leaf_nodes=None, min_impurity_decrease=0.0, min_impurity_split=None, class_weight=None, ccp_alpha=0.0)[source]¶ An extremely randomized tree classifier.
Extratrees differ from classic decision trees in the way they are built. When looking for the best split to separate the samples of a node into two groups, random splits are drawn for each of the
max_features
randomly selected features and the best split among those is chosen. Whenmax_features
is set 1, this amounts to building a totally random decision tree.Warning: Extratrees should only be used within ensemble methods.
Read more in the User Guide.
 Parameters
 criterion{“gini”, “entropy”}, default=”gini”
The function to measure the quality of a split. Supported criteria are “gini” for the Gini impurity and “entropy” for the information gain.
 splitter{“random”, “best”}, default=”random”
The strategy used to choose the split at each node. Supported strategies are “best” to choose the best split and “random” to choose the best random split.
 max_depthint, default=None
The maximum depth of the tree. If None, then nodes are expanded until all leaves are pure or until all leaves contain less than min_samples_split samples.
 min_samples_splitint or float, default=2
The minimum number of samples required to split an internal node:
If int, then consider
min_samples_split
as the minimum number.If float, then
min_samples_split
is a fraction andceil(min_samples_split * n_samples)
are the minimum number of samples for each split.
Changed in version 0.18: Added float values for fractions.
 min_samples_leafint or float, default=1
The minimum number of samples required to be at a leaf node. A split point at any depth will only be considered if it leaves at least
min_samples_leaf
training samples in each of the left and right branches. This may have the effect of smoothing the model, especially in regression.If int, then consider
min_samples_leaf
as the minimum number.If float, then
min_samples_leaf
is a fraction andceil(min_samples_leaf * n_samples)
are the minimum number of samples for each node.
Changed in version 0.18: Added float values for fractions.
 min_weight_fraction_leaffloat, default=0.0
The minimum weighted fraction of the sum total of weights (of all the input samples) required to be at a leaf node. Samples have equal weight when sample_weight is not provided.
 max_featuresint, float, {“auto”, “sqrt”, “log2”} or None, default=”auto”
The number of features to consider when looking for the best split:
If int, then consider
max_features
features at each split.If float, then
max_features
is a fraction andint(max_features * n_features)
features are considered at each split.If “auto”, then
max_features=sqrt(n_features)
.If “sqrt”, then
max_features=sqrt(n_features)
.If “log2”, then
max_features=log2(n_features)
.If None, then
max_features=n_features
.
Note: the search for a split does not stop until at least one valid partition of the node samples is found, even if it requires to effectively inspect more than
max_features
features. random_stateint, RandomState instance or None, default=None
Used to pick randomly the
max_features
used at each split. See Glossary for details. max_leaf_nodesint, default=None
Grow a tree with
max_leaf_nodes
in bestfirst fashion. Best nodes are defined as relative reduction in impurity. If None then unlimited number of leaf nodes. min_impurity_decreasefloat, default=0.0
A node will be split if this split induces a decrease of the impurity greater than or equal to this value.
The weighted impurity decrease equation is the following:
N_t / N * (impurity  N_t_R / N_t * right_impurity  N_t_L / N_t * left_impurity)
where
N
is the total number of samples,N_t
is the number of samples at the current node,N_t_L
is the number of samples in the left child, andN_t_R
is the number of samples in the right child.N
,N_t
,N_t_R
andN_t_L
all refer to the weighted sum, ifsample_weight
is passed.New in version 0.19.
 min_impurity_splitfloat, default=None
Threshold for early stopping in tree growth. A node will split if its impurity is above the threshold, otherwise it is a leaf.
Deprecated since version 0.19:
min_impurity_split
has been deprecated in favor ofmin_impurity_decrease
in 0.19. The default value ofmin_impurity_split
has changed from 1e7 to 0 in 0.23 and it will be removed in 1.0 (renaming of 0.25). Usemin_impurity_decrease
instead. class_weightdict, list of dict or “balanced”, default=None
Weights associated with classes in the form
{class_label: weight}
. If None, all classes are supposed to have weight one. For multioutput problems, a list of dicts can be provided in the same order as the columns of y.Note that for multioutput (including multilabel) weights should be defined for each class of every column in its own dict. For example, for fourclass multilabel classification weights should be [{0: 1, 1: 1}, {0: 1, 1: 5}, {0: 1, 1: 1}, {0: 1, 1: 1}] instead of [{1:1}, {2:5}, {3:1}, {4:1}].
The “balanced” mode uses the values of y to automatically adjust weights inversely proportional to class frequencies in the input data as
n_samples / (n_classes * np.bincount(y))
For multioutput, the weights of each column of y will be multiplied.
Note that these weights will be multiplied with sample_weight (passed through the fit method) if sample_weight is specified.
 ccp_alphanonnegative float, default=0.0
Complexity parameter used for Minimal CostComplexity Pruning. The subtree with the largest cost complexity that is smaller than
ccp_alpha
will be chosen. By default, no pruning is performed. See Minimal CostComplexity Pruning for details.New in version 0.22.
 Attributes
 classes_ndarray of shape (n_classes,) or list of ndarray
The classes labels (single output problem), or a list of arrays of class labels (multioutput problem).
 max_features_int
The inferred value of max_features.
 n_classes_int or list of int
The number of classes (for single output problems), or a list containing the number of classes for each output (for multioutput problems).
feature_importances_
ndarray of shape (n_features,)Return the feature importances.
 n_features_int
The number of features when
fit
is performed. n_outputs_int
The number of outputs when
fit
is performed. tree_Tree instance
The underlying Tree object. Please refer to
help(sklearn.tree._tree.Tree)
for attributes of Tree object and Understanding the decision tree structure for basic usage of these attributes.
See also
ExtraTreeRegressor
An extremely randomized tree regressor.
sklearn.ensemble.ExtraTreesClassifier
An extratrees classifier.
sklearn.ensemble.ExtraTreesRegressor
An extratrees regressor.
Notes
The default values for the parameters controlling the size of the trees (e.g.
max_depth
,min_samples_leaf
, etc.) lead to fully grown and unpruned trees which can potentially be very large on some data sets. To reduce memory consumption, the complexity and size of the trees should be controlled by setting those parameter values.References
 1
P. Geurts, D. Ernst., and L. Wehenkel, “Extremely randomized trees”, Machine Learning, 63(1), 342, 2006.
Examples
>>> from sklearn.datasets import load_iris >>> from sklearn.model_selection import train_test_split >>> from sklearn.ensemble import BaggingClassifier >>> from sklearn.tree import ExtraTreeClassifier >>> X, y = load_iris(return_X_y=True) >>> X_train, X_test, y_train, y_test = train_test_split( ... X, y, random_state=0) >>> extra_tree = ExtraTreeClassifier(random_state=0) >>> cls = BaggingClassifier(extra_tree, random_state=0).fit( ... X_train, y_train) >>> cls.score(X_test, y_test) 0.8947...
Methods
apply
(X[, check_input])Return the index of the leaf that each sample is predicted as.
cost_complexity_pruning_path
(X, y[, …])Compute the pruning path during Minimal CostComplexity Pruning.
decision_path
(X[, check_input])Return the decision path in the tree.
fit
(X, y[, sample_weight, check_input, …])Build a decision tree classifier from the training set (X, y).
Return the depth of the decision tree.
Return the number of leaves of the decision tree.
get_params
([deep])Get parameters for this estimator.
predict
(X[, check_input])Predict class or regression value for X.
Predict class logprobabilities of the input samples X.
predict_proba
(X[, check_input])Predict class probabilities of the input samples X.
score
(X, y[, sample_weight])Return the mean accuracy on the given test data and labels.
set_params
(**params)Set the parameters of this estimator.

apply
(X, check_input=True)[source]¶ Return the index of the leaf that each sample is predicted as.
New in version 0.17.
 Parameters
 X{arraylike, sparse matrix} of shape (n_samples, n_features)
The input samples. Internally, it will be converted to
dtype=np.float32
and if a sparse matrix is provided to a sparsecsr_matrix
. check_inputbool, default=True
Allow to bypass several input checking. Don’t use this parameter unless you know what you do.
 Returns
 X_leavesarraylike of shape (n_samples,)
For each datapoint x in X, return the index of the leaf x ends up in. Leaves are numbered within
[0; self.tree_.node_count)
, possibly with gaps in the numbering.

cost_complexity_pruning_path
(X, y, sample_weight=None)[source]¶ Compute the pruning path during Minimal CostComplexity Pruning.
See Minimal CostComplexity Pruning for details on the pruning process.
 Parameters
 X{arraylike, sparse matrix} of shape (n_samples, n_features)
The training input samples. Internally, it will be converted to
dtype=np.float32
and if a sparse matrix is provided to a sparsecsc_matrix
. yarraylike of shape (n_samples,) or (n_samples, n_outputs)
The target values (class labels) as integers or strings.
 sample_weightarraylike of shape (n_samples,), default=None
Sample weights. If None, then samples are equally weighted. Splits that would create child nodes with net zero or negative weight are ignored while searching for a split in each node. Splits are also ignored if they would result in any single class carrying a negative weight in either child node.
 Returns
 ccp_path
Bunch
Dictionarylike object, with the following attributes.
 ccp_alphasndarray
Effective alphas of subtree during pruning.
 impuritiesndarray
Sum of the impurities of the subtree leaves for the corresponding alpha value in
ccp_alphas
.
 ccp_path

decision_path
(X, check_input=True)[source]¶ Return the decision path in the tree.
New in version 0.18.
 Parameters
 X{arraylike, sparse matrix} of shape (n_samples, n_features)
The input samples. Internally, it will be converted to
dtype=np.float32
and if a sparse matrix is provided to a sparsecsr_matrix
. check_inputbool, default=True
Allow to bypass several input checking. Don’t use this parameter unless you know what you do.
 Returns
 indicatorsparse matrix of shape (n_samples, n_nodes)
Return a node indicator CSR matrix where non zero elements indicates that the samples goes through the nodes.

property
feature_importances_
¶ Return the feature importances.
The importance of a feature is computed as the (normalized) total reduction of the criterion brought by that feature. It is also known as the Gini importance.
Warning: impuritybased feature importances can be misleading for high cardinality features (many unique values). See
sklearn.inspection.permutation_importance
as an alternative. Returns
 feature_importances_ndarray of shape (n_features,)
Normalized total reduction of criteria by feature (Gini importance).

fit
(X, y, sample_weight=None, check_input=True, X_idx_sorted='deprecated')[source]¶ Build a decision tree classifier from the training set (X, y).
 Parameters
 X{arraylike, sparse matrix} of shape (n_samples, n_features)
The training input samples. Internally, it will be converted to
dtype=np.float32
and if a sparse matrix is provided to a sparsecsc_matrix
. yarraylike of shape (n_samples,) or (n_samples, n_outputs)
The target values (class labels) as integers or strings.
 sample_weightarraylike of shape (n_samples,), default=None
Sample weights. If None, then samples are equally weighted. Splits that would create child nodes with net zero or negative weight are ignored while searching for a split in each node. Splits are also ignored if they would result in any single class carrying a negative weight in either child node.
 check_inputbool, default=True
Allow to bypass several input checking. Don’t use this parameter unless you know what you do.
 X_idx_sorteddeprecated, default=”deprecated”
This parameter is deprecated and has no effect. It will be removed in 1.1 (renaming of 0.26).
Deprecated since version 0.24.
 Returns
 selfDecisionTreeClassifier
Fitted estimator.

get_depth
()[source]¶ Return the depth of the decision tree.
The depth of a tree is the maximum distance between the root and any leaf.
 Returns
 self.tree_.max_depthint
The maximum depth of the tree.

get_n_leaves
()[source]¶ Return the number of leaves of the decision tree.
 Returns
 self.tree_.n_leavesint
Number of leaves.

get_params
(deep=True)[source]¶ Get parameters for this estimator.
 Parameters
 deepbool, default=True
If True, will return the parameters for this estimator and contained subobjects that are estimators.
 Returns
 paramsdict
Parameter names mapped to their values.

predict
(X, check_input=True)[source]¶ Predict class or regression value for X.
For a classification model, the predicted class for each sample in X is returned. For a regression model, the predicted value based on X is returned.
 Parameters
 X{arraylike, sparse matrix} of shape (n_samples, n_features)
The input samples. Internally, it will be converted to
dtype=np.float32
and if a sparse matrix is provided to a sparsecsr_matrix
. check_inputbool, default=True
Allow to bypass several input checking. Don’t use this parameter unless you know what you do.
 Returns
 yarraylike of shape (n_samples,) or (n_samples, n_outputs)
The predicted classes, or the predict values.

predict_log_proba
(X)[source]¶ Predict class logprobabilities of the input samples X.
 Parameters
 X{arraylike, sparse matrix} of shape (n_samples, n_features)
The input samples. Internally, it will be converted to
dtype=np.float32
and if a sparse matrix is provided to a sparsecsr_matrix
.
 Returns
 probandarray of shape (n_samples, n_classes) or list of n_outputs such arrays if n_outputs > 1
The class logprobabilities of the input samples. The order of the classes corresponds to that in the attribute classes_.

predict_proba
(X, check_input=True)[source]¶ Predict class probabilities of the input samples X.
The predicted class probability is the fraction of samples of the same class in a leaf.
 Parameters
 X{arraylike, sparse matrix} of shape (n_samples, n_features)
The input samples. Internally, it will be converted to
dtype=np.float32
and if a sparse matrix is provided to a sparsecsr_matrix
. check_inputbool, default=True
Allow to bypass several input checking. Don’t use this parameter unless you know what you do.
 Returns
 probandarray of shape (n_samples, n_classes) or list of n_outputs such arrays if n_outputs > 1
The class probabilities of the input samples. The order of the classes corresponds to that in the attribute classes_.

score
(X, y, sample_weight=None)[source]¶ Return the mean accuracy on the given test data and labels.
In multilabel classification, this is the subset accuracy which is a harsh metric since you require for each sample that each label set be correctly predicted.
 Parameters
 Xarraylike of shape (n_samples, n_features)
Test samples.
 yarraylike of shape (n_samples,) or (n_samples, n_outputs)
True labels for
X
. sample_weightarraylike of shape (n_samples,), default=None
Sample weights.
 Returns
 scorefloat
Mean accuracy of
self.predict(X)
wrt.y
.

set_params
(**params)[source]¶ 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
 **paramsdict
Estimator parameters.
 Returns
 selfestimator instance
Estimator instance.