Add vertical space within legend

Question

I have a large plot with a long legend. Is it possible to add vertical space after certain items?

For instance, if I use the plot shown here as an example, is it possible to add additional vertical space between the items fog-rain and snow-sun (this is of course just an arbitrary example)?

Here is a copy of the code from the altair documentation:

import altair as alt
from vega_datasets import data

source = data.seattle_weather()

alt.Chart(source).mark_bar(
    cornerRadiusTopLeft=3,
    cornerRadiusTopRight=3
).encode(
    x='month(date):O',
    y='count():Q',
    color='weather:N'
)

Thank you very much.

Answer 1

You could do something like this:

source = data.seattle_weather.url

alt.Chart(source).mark_bar().encode(
    x='month(date):O',
    y='count():Q',
    color=alt.Color(
        'weather:N',
        legend=alt.Legend(
            labelExpr='indexof(["snow", "fog"], datum.label) != -1 ? [datum.label, ""] : datum.label'
        )
    )
)

This works by checking if the label datum.label exists in the list ['snow', 'fog'] by asking for the index of the item in that list (which is -1 if the item doesn't exist). If that's the case, we pass a list of two strings, which is how VegaLite/Altair defines multiline strings/titles.

There is also rowPadding which changes the padding between all rows, but I don't think it has access to the column values to do comparisons the way it it done in labelExpr.