Selection Histogram

This chart shows an example of using an interval selection to filter the contents of an attached histogram, allowing the user to see the proportion of items in each category within the selection.

Method syntax

import altair as alt
from vega_datasets import data

source = data.cars()

brush = alt.selection_interval()

points = alt.Chart(source).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color=alt.when(brush).then("Origin:N").otherwise(alt.value("lightgray"))
).add_params(
    brush
)

bars = alt.Chart(source).mark_bar().encode(
    y='Origin:N',
    color='Origin:N',
    x='count(Origin):Q'
).transform_filter(
    brush
)

points & bars

Attribute syntax

import altair as alt
from vega_datasets import data

source = data.cars()

brush = alt.selection_interval()

points = alt.Chart(source).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color=alt.when(brush).then("Origin:N").otherwise(alt.value("lightgray"))
).add_params(
    brush
)

bars = alt.Chart(source).mark_bar().encode(
    y='Origin:N',
    color='Origin:N',
    x='count(Origin):Q'
).transform_filter(
    brush
)

points & bars
# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.