How to add text on interactive Scatter on Altair? - text

Question

I try to adapt the Selection Detail Example from altair doc (https://altair-viz.github.io/gallery/select_detail.html#selection-detail-example).
I won't detailed my Dataframe structure which is identical with the one from the example (included variable names).
The native code is working well :
# Data is prepared, now make a chart
selector = alt.selection_single(empty='all', fields=['id'])
base = alt.Chart(data).properties(
width=250,
height=250
).add_selection(selector)
points = base.mark_point(filled=True, size=200,opacity=0.9).encode(
x=alt.X('mean(y)',title='Durée de perception',scale=alt.Scale(domain=(11, 23))),
y=alt.Y('mean(x)',title='Taux de marge (%PM)'),
color=alt.condition(selector, 'id:O', alt.value('lightgray')),
tooltip = ['mean(y)','mean(x)']
)
timeseries = base.mark_bar(opacity=1).encode(
x=alt.X('time', title='Items'),
y=alt.Y('value', scale=alt.Scale(domain=(-1, 1)),stack=None),
color=alt.Color('id:O',scale=alt.Scale(domain=domain, range=range_))
#, legend=None)
).transform_filter(
selector
)
points | timeseries
No problem at this stage even if it could be useful to hide all the bars on right chart when no selection is made on the right chart (don't know if it's possible ?)
After that I try to add text to the scatter plot adding this at the end of the code :
text = points.mark_text(dy=-5).encode(
x=alt.X('mean(y)',title='Durée de perception',scale=alt.Scale(domain=(11, 23))),
y=alt.Y('mean(x)',title='NBV (%CA)'),
text='id:O'
)
(points + text) | timeseries
which leads to the following error message :
Javascript Error: Duplicate signal name: "selector094_tuple"
This usually means there's a typo in your chart specification. See the javascript console for the full traceback.
If you have any idea on how to do, i would be grateful
Thanks

Answer 1

The issue is that you cannot add the same selection to two different layers, which you do implicitly by deriving text from points. Try this instead:
text = alt.Chart(data).mark_text(dy=-5).encode(
x=alt.X('mean(y)',title='Durée de perception',scale=alt.Scale(domain=(11, 23))),
y=alt.Y('mean(x)',title='NBV (%CA)'),
text='id:O'
)
(points + text) | timeseries