Visualization

Data in a Polars DataFrame can be visualized using common visualization libraries.

We illustrate plotting capabilities using the Iris dataset. We scan a CSV and then do a group-by on the species column and get the mean of the petal_length.

Python

import polars as pl

path = "docs/data/iris.csv"

df = pl.scan_csv(path).group_by("species").agg(pl.col("petal_length").mean()).collect()
print(df)

shape: (3, 2)
┌────────────┬──────────────┐
│ species    ┆ petal_length │
│ ---        ┆ ---          │
│ str        ┆ f64          │
╞════════════╪══════════════╡
│ Versicolor ┆ 4.26         │
│ Setosa     ┆ 1.462        │
│ Virginica  ┆ 5.552        │
└────────────┴──────────────┘

Built-in plotting with hvPlot

Polars has a plot method to create interactive plots using hvPlot.

Python

df.plot.bar(
    x="species",
    y="petal_length",
    width=650,
)

Matplotlib

To create a bar chart we can pass columns of a DataFrame directly to Matplotlib as a Series for each column. Matplotlib does not have explicit support for Polars objects but Matplotlib can accept a Polars Series because it can convert each Series to a numpy array, which is zero-copy for numeric data without null values.

Python

import matplotlib.pyplot as plt

plt.bar(x=df["species"], height=df["petal_length"])

Seaborn, Plotly & Altair

Seaborn, Plotly & Altair can accept a Polars DataFrame by leveraging the dataframe interchange protocol, which offers zero-copy conversion where possible.

Seaborn

Python

import seaborn as sns
sns.barplot(
    df,
    x="species",
    y="petal_length",
)

Plotly

Python

import plotly.express as px

px.bar(
    df,
    x="species",
    y="petal_length",
    width=400,
)

Altair

Python

import altair as alt

alt.Chart(df, width=700).mark_bar().encode(x="species:N", y="petal_length:Q")