Text labeling not matching stacked bar chart

Hello there and thanks for this great framework! I have an issue with the following bar chart: Click

Note that I added the red rectangle to highlight a problem: some text labels do not match the bar below. So in this case the 55% and the 41% should be switched around. When I enable tool tips then I can see that the correct value is actually used by altair for the bar plot but not for the label. Strangely enough this only happens for some values…

It is created by this code:

base = alt.Chart().mark_bar().encode(
    x=alt.X("value:Q", stack='normalize',axis=alt.Axis(format='%', title='Percentage Reacted Normalized')),
    y=alt.Y(md_db.param_boxize+':O', axis=alt.Axis(title='Box Size')),
    tooltip=['value', 'value_norm:Q', 'value_ref_ratio:Q','variable:N', md_db.param_boxize+ ':O'] + [md_db.param_react + str(n) + ':N' for n in range(2)],
    
)
bars = base.encode(
    color=alt.Color('variable:N'),
)
text = base.mark_text(
    dx=-10,
    angle=0,
    color='black',
).encode(
    text=alt.Text('value_norm:Q',format='.0%'),
)
alt.layer(bars, text).facet(
    column=alt.Column('type:N'),
    row=alt.Row(md_db.param_diff_col+':N', header=alt.Header(labelAngle=0)),
    data=df_merge
)

Unfortunately I cannot attach dummy data right now but will do so if requested.

[jakevdp]

For what it’s worth, here’s how you can push the data manipulations into the chart’s transform specification:

df = data.barley()

base = alt.Chart(df).transform_joinaggregate(
    yield_sum='sum(yield)',
    groupby=['year', 'variety']
).transform_calculate(
    yield_norm='datum.yield / datum.yield_sum'  
).mark_bar().encode(
    x=alt.X('yield:Q', stack='normalize'),
    y=alt.Y('variety:N'),
    tooltip=['yield:Q', 'variety:N', 'year:O', 'yield_norm:Q'],
    order='site:N'
)

bars = base.encode(
    detail='site:N',
    color='site:N',
)

text = base.mark_text(dx=-15, dy=3).encode(
    text=alt.Text('yield_norm:Q', format='.0%'),
)

alt.layer(bars, text).facet(column=alt.Column('year:O'))

[jakevdp]

I think that error indicates that you’re using Altair version 3.0. Update to the latest release (3.1), and the code should work.

If you need to stick with Altair version 3.0 for some reason, you can specify the data in the facet method, as you did in your original snippet.