Selection zorder#
This example shows how to bring selected points to the front/foreground by using a condition to change the point’s (z)order as it is hovered over with the pointer. This prevents that the selected points are obscured by those that are not selected.
import altair as alt
from vega_datasets import data
cars = data.cars.url
hover = alt.selection_point(on='pointerover', nearest=True, empty=False)
chart = alt.Chart(cars, title='Selection obscured by other points').mark_circle(opacity=1).encode(
x='Horsepower:Q',
y='Miles_per_Gallon:Q',
color=alt.condition(hover, alt.value('coral'), alt.value('lightgray')),
size=alt.condition(hover, alt.value(300), alt.value(30))
).add_params(
hover
)
chart | chart.encode(
order=alt.condition(hover, alt.value(1), alt.value(0))
).properties(
title='Selection brought to front'
)
import altair as alt
from vega_datasets import data
cars = data.cars.url
hover = alt.selection_point(on='pointerover', nearest=True, empty=False)
chart = alt.Chart(cars, title='Selection obscured by other points').mark_circle(opacity=1).encode(
x='Horsepower:Q',
y='Miles_per_Gallon:Q',
color=alt.condition(hover, alt.value('coral'), alt.value('lightgray')),
size=alt.condition(hover, alt.value(300), alt.value(30))
).add_params(
hover
)
chart | chart.encode(
order=alt.condition(hover, alt.value(1), alt.value(0))
).properties(
title='Selection brought to front'
)
# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.