Create label encoder across multiple columns

You can apply label encoder to all columns using the ColumnTransformer step.

This demonstrates how to use properly transform columns using neuraxle.

For more info, see the thread here.

import numpy as np
import pandas
from sklearn.preprocessing import LabelEncoder

from neuraxle.steps.column_transformer import ColumnTransformer
from neuraxle.steps.loop import FlattenForEach

# Discussion:
# https://stackoverflow.com/questions/24458645/label-encoding-across-multiple-columns-in-scikit-learn
df = pandas.DataFrame({
    'pets': ['cat', 'dog', 'cat', 'monkey', 'dog', 'dog'],
    'owner': ['Champ', 'Ron', 'Brick', 'Champ', 'Veronica', 'Ron'],
    'location': ['San_Diego', 'New_York', 'New_York', 'San_Diego', 'San_Diego', 'New_York']
})


def _apply_same_encoder_to_all_columns():
    """
    One shared LabelEncoder will be applied on all the data to encode it.
    """
    p = FlattenForEach(LabelEncoder(), then_unflatten=True)

    p, predicted_output = p.fit_transform(df.values)

    expected_output = np.array([
        [6, 7, 6, 8, 7, 7],
        [1, 3, 0, 1, 5, 3],
        [4, 2, 2, 4, 4, 2]
    ]).transpose()
    assert np.array_equal(predicted_output, expected_output)


def _apply_different_encoders_to_columns():
    """
    One standalone LabelEncoder will be applied on the pets,
    and another one will be shared for the columns owner and location.
    """
    p = ColumnTransformer([
        # A different encoder will be used for column 0 with name "pets":
        (0, FlattenForEach(LabelEncoder(), then_unflatten=True)),
        # A shared encoder will be used for column 1 and 2, "owner" and "location":
        ([1, 2], FlattenForEach(LabelEncoder(), then_unflatten=True)),
    ], n_dimension=2)

    p, predicted_output = p.fit_transform(df.values)

    expected_output = np.array([
        [0, 1, 0, 2, 1, 1],
        [1, 3, 0, 1, 5, 3],
        [4, 2, 2, 4, 4, 2]
    ]).transpose()
    assert np.array_equal(predicted_output, expected_output)


def main():
    _apply_same_encoder_to_all_columns()
    _apply_different_encoders_to_columns()


if __name__ == "__main__":
    main()