class dask_ml.preprocessing.Categorizer(categories: Optional[dict] = None, columns: Optional[pandas.core.indexes.base.Index] = None)

Transform columns of a DataFrame to categorical dtype.

This is a useful pre-processing step for dummy, one-hot, or categorical encoding.

categoriesmapping, optional

A dictionary mapping column name to instances of pandas.api.types.CategoricalDtype. Alternatively, a mapping of column name to (categories, ordered) tuples.

columnssequence, optional

A sequence of column names to limit the categorization to. This argument is ignored when categories is specified.


The columns that were categorized. Useful when categories is None, and we detect the categorical and object columns


A dictionary mapping column names to dtypes. For pandas>=0.21.0, the values are instances of pandas.api.types.CategoricalDtype. For older pandas, the values are tuples of (categories, ordered).


This transformer only applies to dask.DataFrame and pandas.DataFrame. By default, all object-type columns are converted to categoricals. The set of categories will be the values present in the column and the categoricals will be unordered. Pass dtypes to control this behavior.

All other columns are included in the transformed output untouched.

For dask.DataFrame, any unknown categoricals will become known.


>>> df = pd.DataFrame({"A": [1, 2, 3], "B": ['a', 'a', 'b']})
>>> ce = Categorizer()
>>> ce.fit_transform(df).dtypes
A       int64
B    category
dtype: object
>>> ce.categories_
{'B': CategoricalDtype(categories=['a', 'b'], ordered=False)}

Using CategoricalDtypes for specifying the categories:

>>> from pandas.api.types import CategoricalDtype
>>> ce = Categorizer(categories={"B": CategoricalDtype(['a', 'b', 'c'])})
>>> ce.fit_transform(df).B.dtype
CategoricalDtype(categories=['a', 'b', 'c'], ordered=False)


fit(X[, y])

Find the categorical columns.

fit_transform(X[, y])

Fit to data, then transform it.


Get parameters for this estimator.

set_output(*[, transform])

Set output container.


Set the parameters of this estimator.

transform(X[, y])

Transform the columns in X according to self.categories_.

__init__(categories: Optional[dict] = None, columns: Optional[pandas.core.indexes.base.Index] = None)