Altair: Plotting legend below chart

[maxgerma]

Dear all,

first I want to say that I love Altair's logic of creating charts!
Now the issue: I have concatenated several charts to a 2x2 plot and need the (single) legend to be placed below the entire 2x2 plot. Is there a way of doing so in Altair? I really don't want to have to redo plotting in matplotlib (using fig.legend or bbox_to_anchor as proposed for such cases) or other packages.

Best, Maximilian

[jakevdp]

You can see the available options for controlling the legend appearance in the documentation for alt.Legend, which should be passed as an argument to the color encoding, for example:

chart.encode(
    #...
    color=alt.Color('value', legend=alt.Legend(orient='right'))
    #...
)

The available options for controlling the legend appearance are relatively limited in the current release of Altair; these will be greatly expanded in Altair v3, which is built on Vega-Lite 3 (you can read about the options in Vega-Lite 3 in the vega-lite docs).

Once vega-lite 3 is released, we will work on an Altair release that will also provide these options.

[maxgerma]

Thanks for the prompt reply. I am looking forward to the next release then.

[jakevdp]

In Altair 3, the current release, you can use orient='bottom'. For example

import altair as alt
from vega_datasets import data
cars = data.cars()

alt.Chart(cars).mark_point().encode(
  x='Horsepower',
  y='Miles_per_Gallon',
  color='Origin'
).configure_legend(
  orient='bottom'
)