Repeated charts

Question

I'm trying to make a plot:

import altair as alt
from vega_datasets import data

movies = data.movies.url

base = alt.Chart(movies).mark_bar().encode(
alt.Y('count()')).properties(
    width=200,
    height=150
)

chart = alt.vconcat()
for x_encoding in ['IMDB_Rating:Q', 'IMDB_Votes:Q']:
    row = alt.hconcat()
    for maxbins_encoding in [10, 50]:
        row |= base.encode(alt.X(x_encoding, 
        type='quantitative',
        bin=Bin(maxbins=maxbins_encoding)))
    chart &= row
chart

This works. Then I'm trying to use alt.repeat():

alt.Chart(vega_datasets.data.movies.url).mark_bar().encode(
    alt.X(alt.repeat("row"), type='quantitative',  
    bin=Bin(maxbins=alt.repeat('column'))),
    alt.Y('count()')
).properties(
    width=200,
    height=150
).repeat(
    row=['IMDB_Rating', 'IMDB_Votes'],
    column=[10, 50]
)

It gives me this error message:

SchemaValidationError: Invalid specification

        altair.vegalite.v3.schema.core.BinParams->maxbins, validating 'type'

        {'repeat': 'column'} is not of type 'number'

So I must have missed something. Does it have something to do with using repeat() in the bin=Bin() argument other than directly using it in the encode()?

Answer 1

Unfortunately, repeat entries cannot be used for bin parameters. The only parameters that use repeat in Vega-Lite are column names passed to encodings, so your initial approach of looping is probably best.

If you want to take advantage of repeats for the x encodings, you could do something like this:

def make_column(maxbins):
    return alt.Chart(movies).mark_bar().encode(
        alt.X(alt.repeat("row"), type='quantitative',  
              bin=alt.Bin(maxbins=maxbins)),
        alt.Y('count()')
    ).properties(
        width=200,
        height=150
    ).repeat(
        row=['IMDB_Rating', 'IMDB_Votes'],
    )

make_column(10) | make_column(50)