Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

Adding text to bar chart throws 'data is a required property' error

See original GitHub issue

When I run this code, I get a ‘data is a required property’ error (pasted below the code). When I just try to run the bar graph with data specified within Chart() it works.

bars = alt.Chart().mark_bar(stroke='transparent').encode(
    alt.X('model', scale=alt.Scale(rangeStep=12), axis=alt.Axis(title='')),
    alt.Y('ratio:Q', axis=alt.Axis(title='ratio', grid=False)),
    color=alt.Color('model:N', scale=alt.Scale(range=["#EA98D2", "#659CCA", '#5bb3a4'])),
    column='time:O', 
)

text = alt.Chart().mark_text(
    align='left',
    baseline='middle'
).encode(
    y = alt.Y('ratio'), 
    x = 'model',
    text='ratio')

alt.layer(bars, text, data=df_concat).configure(
    legend=LegendConfig(labelFontSize=16, titleFontSize=16, symbolSize=100, labelFont='Lato'), axis=AxisConfig(labelFontSize=16, tickSize=16, labels=True, titleFontSize=16))

Error Message:

SchemaValidationError: Invalid specification

        altair.vegalite.v2.api.Chart, validating 'required'

        'data' is a required property

Issue Analytics

State:
Created 5 years ago
Comments:8 (3 by maintainers)

Top GitHub Comments

1reaction

Alcampopianocommented, Oct 29, 2018

@lcyraphael Off the top of my head I think you want to configure the header if I understand correctly.

import altair as alt
from altair.expr import datum
from vega_datasets import data
iris = data.iris.url


alt.Chart(iris).mark_point().encode(
    x='petalLength:Q',
    y='petalWidth:Q',
    color='species:N'
).properties(
    width=180,
    height=180
).facet(
    column='species:N'
).configure_header(titleFontSize=40, labelFontSize=40

)

visualization 52

1reaction

jakevdpcommented, Oct 9, 2018

Ah, I see now. The error is unfortunately not particularly informative here, but the core issue is that you cannot use a faceted chart within a layer (from the perspective of the renderer, it’s ill-defined what the user intends in that case).

The alternative is to create a layered chart first, and then facet it. For example:

import altair as alt
import pandas as pd

df_concat = pd.DataFrame({
'time': [87, 88, 89, 87, 88, 89, 87, 88, 89],
'ratio': [0.27, 0.39, 0.35, 0.39, 0.51, 0.38, 0.20, 0.35, 0.47],
'model': ['b3b', 'b3b', 'b3b', 'baseline', 'baseline', 'baseline', 'truth', 'truth', 'truth']
})

bars = alt.Chart().mark_bar(stroke='transparent').encode(
    alt.X('model', scale=alt.Scale(rangeStep=12), axis=alt.Axis(title='')),
    alt.Y('ratio:Q', axis=alt.Axis(title='ratio', grid=False)),
    color=alt.Color('model:N', scale=alt.Scale(range=["#EA98D2", "#659CCA", '#5bb3a4'])),
)

text = alt.Chart().mark_text(
    align='left',
    baseline='middle'
).encode(
    y = alt.Y('ratio'), 
    x = 'model',
    text='ratio'
)

alt.layer(bars, text, data=df_concat).facet(
    column='time:O'
).configure(
    legend=alt.LegendConfig(labelFontSize=16, titleFontSize=16, symbolSize=100, labelFont='Lato'),
    axis=alt.AxisConfig(labelFontSize=16, tickSize=16, labels=True, titleFontSize=16)
)

visualization