kra

A set of useful tools to work with polars, providing convenient extensions for DataFrame manipulation, column operations, label encoding, and more.

Installation

Build and install the Rust extension and Python API using maturin:

pip install maturin
maturin develop

Or, for development and testing:

pip install nox
nox

Features

• DataFrame and Series extensions: Add new methods to polars DataFrames and Series.
• Column utilities: Easily rename, check, and transform DataFrame columns.
• Label encoding: Encode string labels as categorical/integer values.
• Dict-of-dicts conversion: Convert between DataFrames and nested dictionaries.

Example Use Cases

1. Dict-of-Dicts Conversion

Convert a DataFrame to a dict of dicts using a column as the key:

import polars as pl
import kra

df = pl.DataFrame({
    "id": [1, 2, 3],
    "name": ["Alice", "Bob", "Charlie"]
})

dod = df.to_dod("id")
# {1: {'id': 1, 'name': 'Alice'}, 2: {'id': 2, 'name': 'Bob'}, ...}

# Convert back:
df2 = kra.from_dod(dod, "id")

2. Column Name Transformations

Transform column names to different cases:

import polars as pl
import kra

df = pl.DataFrame({
    "First Name": [1, 2],
    "Last Name": [3, 4]
})

df_lower = df.cols.to_lowercase()
df_camel = df.cols.to_camelcalse()
df_snake = df.cols.to_snakecase()

3. Label Encoding

Encode string labels as integers:

import polars as pl
import kra

df = pl.DataFrame({
    "label": ["cat", "dog", "cat", "bird"]
})

# Series API
encoded = df["label"].label.encode()

# Expression API (for use in with_columns, etc.)
df2 = df.with_columns(
    pl.col("label").label.encode().alias("encoded_label")
)

4. DataFrame Utilities

Drop columns of type Null:

import polars as pl
import kra

df = pl.DataFrame({
    "a": [1, 2, 3],
    "b": [None, None, None]
})

df_clean = df.drop_null_cols()

5. From Array-like

Create a DataFrame from a numpy array:

import kra
import numpy as np

data = np.array([[1, 2], [3, 4]])
df = kra.from_arraylike(data, schema=["x", "y"], orient="col")

API Reference

• kra.from_dod: Create DataFrame from dict of dicts.
• kra.to_dod: Convert DataFrame to dict of dicts.
• kra.Cols: DataFrame column utilities (access via df.cols).
• kra.LabelSeries: Series label encoding (access via series.label).
• kra.LabelExpr: Expression label encoding (access via pl.col(...).label).
• kra.drop_null_cols: Remove columns of type Null.
• kra.from_arraylike: Create DataFrame from array-like objects.

For more, see the intro.ipynb notebook.

Rust Extension

kra includes a Rust extension for fast label encoding, accessible via the Python API.

License

MIT License. See LICENSE for details.