Histogram with Adjustable Bin Size

This example shows a 2D histogram heatmap whose bin size can be changed with a slider. Vega-Lite does not allow a parameter to drive maxbins directly, so we draw one layer per available bin count and only show the layer that matches the slider value.

Method syntax

import altair as alt
from altair.datasets import data

source = data.movies.url

maxbins_options = [10, 20, 30, 40, 50, 60]

slider = alt.binding_range(
    min=min(maxbins_options),
    max=max(maxbins_options),
    step=10,
    name="Max bins ",
)
maxbins = alt.param(name="maxbins", value=30, bind=slider)

layers = [
    alt.Chart(source)
    .mark_rect()
    .encode(
        alt.X("IMDB Rating:Q")
        .bin(maxbins=n)
        .scale(zero=True)
        .axis(format="d", title="IMDB Rating"),
        alt.Y("Rotten Tomatoes Rating:Q")
        .bin(maxbins=n)
        .axis(format="d", title="Rotten Tomatoes Rating"),
        alt.Color("count():Q").scale(scheme="greenblue"),
    )
    .transform_filter(f"maxbins === {n}")
    for n in maxbins_options
]

alt.layer(*layers).add_params(maxbins)

Attribute syntax

import altair as alt
from altair.datasets import data

source = data.movies.url

maxbins_options = [10, 20, 30, 40, 50, 60]

slider = alt.binding_range(
    min=min(maxbins_options),
    max=max(maxbins_options),
    step=10,
    name="Max bins ",
)
maxbins = alt.param(name="maxbins", value=30, bind=slider)

layers = [
    alt.Chart(source).mark_rect().encode(
        x=alt.X(
            "IMDB Rating:Q",
            bin=alt.Bin(maxbins=n),
            scale=alt.Scale(zero=True),
            axis=alt.Axis(format="d", title="IMDB Rating"),
        ),
        y=alt.Y(
            "Rotten Tomatoes Rating:Q",
            bin=alt.Bin(maxbins=n),
            axis=alt.Axis(format="d", title="Rotten Tomatoes Rating"),
        ),
        color=alt.Color("count():Q", scale=alt.Scale(scheme="greenblue")),
    ).transform_filter(f"maxbins === {n}")
    for n in maxbins_options
]

alt.layer(*layers).add_params(maxbins)