Change single color in Altair plot-CodePudding

Is there a way to change the color of just a single group in Altair plot, while leaving the rest the same? I like the default color scheme fine, but there is one group I want to change the color for.

For example, in a scatter-plot like this:

import altair as alt
from vega_datasets import data

iris = data.iris()

alt.Chart(iris).mark_point().encode(
    x='petalWidth',
    y='petalLength',
    color=alt.Color('species')
)

I would like to change the color of 'versicolor' to black, without changing the rest.

I know from the documentation that you can specify your own color scheme, or assign colors to each one of the groups, like so:

domain = ['setosa', 'versicolor', 'virginica']
range_ = ['red', 'green', 'blue']

alt.Chart(iris).mark_point().encode(
    x='petalWidth',
    y='petalLength',
    color=alt.Color('species', scale=alt.Scale(domain=domain, range=range_))
)

But I cannot find a simple way to change the color for a single species without affecting the rest of the colors.

CodePudding user response：

One way to do this is with an alt.condition, although the updated color will not appear in the legend:

import altair as alt
from vega_datasets import data

iris = data.iris()

alt.Chart(iris).mark_point().encode(
    x='petalWidth',
    y='petalLength',
    color=alt.condition("datum.species == 'setosa'", alt.value('yellow'), alt.Color('species'))
)

If you want to change the color and have it reflected in the legend, the only way to do so is to use a custom scale as you did in your question.