faceted layered chart errors out while "validating 'anyOf'"

I was trying to reproduce a custom non-altair/vega chart I saw online when I ran into some trouble.

When faceting a chart then layering it - produces this error:

---------------------------------------------------------------------------
SchemaValidationError                     Traceback (most recent call last)
C:\Users\jthomp261\AppData\Local\Continuum\anaconda3\envs\data_analysis\lib\site-packages\altair\vegalite\v2\api.py in to_dict(self, *args, **kwargs)
    338         if dct is None:
    339             kwargs['validate'] = 'deep'
--> 340             dct = super(TopLevelMixin, copy).to_dict(*args, **kwargs)
    341 
    342         if is_top_level:

C:\Users\jthomp261\AppData\Local\Continuum\anaconda3\envs\data_analysis\lib\site-packages\altair\utils\schemapi.py in to_dict(self, validate, ignore, context)
    252                 self.validate(result)
    253             except jsonschema.ValidationError as err:
--> 254                 raise SchemaValidationError(self, err)
    255         return result
    256 

SchemaValidationError: Invalid specification

        altair.vegalite.v2.api.LayerChart->layer->items, validating 'anyOf'

Here is the non-faceted that works:

import altair as alt
from vega_datasets import data

stocks = data.stocks()
# get the price on the most recent date for the point chart
stocks_max = pd.merge(stocks.groupby('symbol')['date'].max().reset_index(),
                      stocks, on=['symbol', 'date'], how='left')

point = alt.Chart(stocks_max).mark_point().encode(
    x='date:T',
    y='price',
    color='symbol')

line = alt.Chart(stocks).mark_line(color='red').encode(
    x='date:T',
    y='price',
    color='symbol')

line+point

Now when I change the

color='symbol'

to

row='symbol'

so that the bottom part looks like this:

point = alt.Chart(stocks_max).mark_point().encode(
    x='date:T',
    y='price',
    row='symbol')

line = alt.Chart(stocks).mark_line(color='red').encode(
    x='date:T',
    y='price',
    row='symbol')

line+point

I then get the error mentioned above.

I have searched on this repo and on vega-lite’s repo for layered facets with many results of errors but they were all different from this one. I may be missing something basic here.

Note: this is not the completed chart, was was going to layer on another bar plot to get some other effect, but hit this roadblock on the way.

[anitagraser]

It would be great to add this limitation as a side note to the example at https://altair-viz.github.io/gallery/choropleth_repeat.html. As soon as the user tries to add another map layer, the chart is broken and the error message is rather cryptic. Took me a while to find this issue report.

[gh-owestesson]

@jakevdp I the transform_lookup is what makes most sense. Thanks!