Stacked bar chart rendering bug in the presence of negative values

Hi,

Really enjoying Altair but I’ve run into a bug when attempt to display stacked bars, some of which contain negative values.

Here is a minimal test case that demonstrates the problem.

import pandas as pd
from altair import Chart

data = pd.DataFrame({'amount': [-2000, 3000, 2000, 4000, 3000, 5000, 1000, 2000],
 'quarter': ['Q1', 'Q1', 'Q2', 'Q2', 'Q3', 'Q3', 'Q1', 'Q1'],
 'type': ['N', 'C', 'N', 'C', 'N', 'C', 'N', 'C'],
 'year': [2016, 2016, 2016, 2016, 2016, 2016, 2017, 2017]})

Chart(data).mark_bar().encode(
    color='type:N',
    column='quarter:O',
    x='year:N',
    y='sum(amount):Q',
)

Which produces this view:

If you remove the sum() aggregation from the y axis, the negative values are displayed but you lose the stacking.

Chart(data).mark_bar().encode(
    color='type:N',
    column='quarter:O',
    x='year:N',
    y='amount:Q',
)

Which looks like this:

Anyone else run into this issue?

[jheer]

The latest version of Vega (3.0.0-beta.26) has an updated stack transform that can properly handle negative numbers. As a result, Vega-Lite 2.0 will ultimately “do the right thing” here.

[ellisonbg]

Thanks @jheer and @kanitw for the clarification. Closing as question/vega-lite