Select

Selects features.

This can be used in a pipeline when you want to select certain features. The transform_one method is pure, and therefore returns a fresh new dictionary instead of filtering the specified keys from the input.

Parameters

• keys (Tuple[Hashable])

  Key(s) to keep.

Examples

>>> from river import compose

>>> x = {'a': 42, 'b': 12, 'c': 13}
>>> compose.Select('c').transform_one(x)
{'c': 13}

You can chain a selector with any estimator in order to apply said estimator to the desired features.

>>> from river import feature_extraction as fx

>>> x = {'sales': 10, 'shop': 'Ikea', 'country': 'Sweden'}

>>> pipeline = (
...     compose.Select('sales') |
...     fx.PolynomialExtender()
... )
>>> pipeline.transform_one(x)
{'sales': 10, 'sales*sales': 100}

This transformer also supports mini-batch processing:

>>> import random
>>> from river import compose

>>> random.seed(42)
>>> X = [{"x_1": random.uniform(8, 12), "x_2": random.uniform(8, 12)} for _ in range(6)]
>>> for x in X:
...     print(x)
{'x_1': 10.557707193831535, 'x_2': 8.100043020890668}
{'x_1': 9.100117273476478, 'x_2': 8.892842952595291}
{'x_1': 10.94588485665605, 'x_2': 10.706797949691644}
{'x_1': 11.568718270819382, 'x_2': 8.347755330517664}
{'x_1': 9.687687278741082, 'x_2': 8.119188877752281}
{'x_1': 8.874551899214413, 'x_2': 10.021421152413449}

>>> import pandas as pd
>>> X = pd.DataFrame.from_dict(X)

You can then call transform_many to transform a mini-batch of features:

>>> compose.Select('x_2').transform_many(X)
    x_2
0   8.100043
1   8.892843
2  10.706798
3   8.347755
4   8.119189
5  10.021421

Methods

clone

Return a fresh estimator with the same parameters.

The clone has the same parameters but has not been updated with any data. This works by looking at the parameters from the class signature. Each parameter is either - recursively cloned if it's a River classes. - deep-copied via copy.deepcopy if not. If the calling object is stochastic (i.e. it accepts a seed parameter) and has not been seeded, then the clone will not be idempotent. Indeed, this method's purpose if simply to return a new instance with the same input parameters.

learn_many

Update with a mini-batch of features.

A lot of transformers don't actually have to do anything during the learn_many step because they are stateless. For this reason the default behavior of this function is to do nothing. Transformers that however do something during the learn_many can override this method.

Parameters

• X (pandas.core.frame.DataFrame)
• kwargs

Returns

Transformer: self

learn_one

Update with a set of features x.

A lot of transformers don't actually have to do anything during the learn_one step because they are stateless. For this reason the default behavior of this function is to do nothing. Transformers that however do something during the learn_one can override this method.

Parameters

• x (dict)
• kwargs

Returns

Transformer: self

transform_many

Transform a mini-batch of features.

Parameters

• X (pandas.core.frame.DataFrame)

Returns

DataFrame: A new DataFrame.

transform_one

Transform a set of features x.

Parameters

• x (dict)

Returns

dict: The transformed values.