How to draw scatter+line facet chart in altair

[HotWesley]

How to draw scatter+line facet chart in altair

below is my code
`def correlation_result_plot(source):

chart_title = alt.TitleParams('-'.join([source['item_id1'].iloc[0], source['item_id2'].iloc[0]]), anchor='middle')
source['key'] = source['item_id1'].astype(str) + '-' + source['item_id2'].astype(str)
chart = alt.Chart(source).mark_point().encode(
        x=alt.X('value1', type='quantitative', scale=alt.Scale(zero=False)),
        y=alt.Y('value2', type='quantitative', scale=alt.Scale(zero=False)),
        color=alt.Color('item_id2', legend=None)).properties(width=230, height=230).resolve_scale(x='independent', y='independent')

line = chart.transform_regression('value1', 'value2').mark_line(color='red')

chart = chart.facet(column='key', columns=4)

return (chart + line).properties(title=chart_title)`

then an error has occurred below
raise ValueError( ValueError: Faceted charts cannot be layered. Instead, layer the charts before faceting.

how can i resolve it.... thanks in advance!

[joelostblom]

The error message points you in the right direction: you need to do faceting after layering, rather than before. For your spec, that means adding line and chart together before using the facet method on the layered spec. See this section of the docs for an example https://altair-viz.github.io/user_guide/compound_charts.html#faceted-charts

Duplicate of #3310

[HotWesley]

thank you for your answer. I modify my code like beloq.
`def test(source):

chart_title = alt.TitleParams('-'.join([source['item_id1'].iloc[0], source['item_id2'].iloc[0]]), anchor='middle')
source['key'] = source['item_id1'].astype(str) + '-' + source['item_id2'].astype(str)
chart = alt.Chart(source).mark_point().encode(
        x=alt.X('value1', type='quantitative', scale=alt.Scale(zero=False)),
        y=alt.Y('value2', type='quantitative', scale=alt.Scale(zero=False)),
        color=alt.Color('item_id2', legend=None)).properties(width=230, height=230).resolve_scale(x='independent', y='independent')

line = chart.transform_regression('value1', 'value2').mark_line(color='red')

return alt.layer(chart, line).facet('item_id2:N', columns=4)`

then this error has occurred.
`altair.utils.schemapi.SchemaValidationError: Multiple errors were found.

Error 1: Spec has no parameter named 'mark'

Existing parameter names are:
args

See the help for `Spec` to read the full description of these parameters

Error 2: Spec has no parameter named 'mark'

Existing parameter names are:
args

See the help for `Spec` to read the full description of these parameters`

[joelostblom]

Interesting, I think you found a bug which I reported in more detail #3502. As a workaround, you can move resolve_scale outside layer or facet (depending on what you want to resolve, likey facet)