`selection_point` fails schema validation

[jpn--]

What happened?

I am trying to create an interactive figure that filters on data by iteration, but I am getting a SchemaValidationError:

SchemaValidationError: '2000' is an invalid value foriteration. Valid values are of type 'array'.

If I copy the published example from here, and run it, it works fine. But if I simply change the name of the data column "year" to "iteration", I can reproduce the failure.

import altair as alt
from vega_datasets import data
import pandas as pd

# read to pandas DataFrame 
df = pd.read_json(data.population.url)

# change column name "year" to "iteration"
df = df.rename(columns={"year": "iteration"})

# code below otherwise identical to example except changing "year" to "iteration"
select_year = alt.selection_point(
    name="Year",
    fields=["iteration"],
    bind=alt.binding_range(min=1900, max=2000, step=10, name="Year"),
    value={"iteration": 2000},
)

alt.Chart(df).mark_bar().encode(
    alt.X("sex:N").title('').axis(labels=False, ticks=False),
    alt.Y("people:Q").scale(domain=(0, 12000000)).title("Population"),
    alt.Color("sex:N")
        .scale(domain=("Male", "Female"), range=["steelblue", "salmon"])
        .title("Sex"),
    alt.Column("age:O").title("Age")
).properties(
    width=20,
    title="U.S. Population by Age and Sex"
).add_params(
    select_year
).transform_calculate(
    "sex", alt.expr.if_(alt.datum.sex == 1, "Male", "Female")
).transform_filter(
    select_year
).configure_facet(
    spacing=8
)

What would you like to happen instead?

The selection should work and not depend on the variable name literally being "year".

Which version of Altair are you using?

5.4.1

[dangotbanned]

# change column name "year" to "iteration"
# df.rename(columns={"year": "iteration"})
source = df.rename(columns={"year": "iteration"})

@jpn-- in your code block, alt.Chart references source - but that isn't the same as your renamed df.

Does this fix the validation error?

[jpn--]

@dangotbanned Apologies, I had a bad copy-and-paste job into the issue. I've corrected the code above, the error still persists; and actually, I've found the error occur even before my (now fixed) bug. I can reproduce the SchemaValidationError with just this:

import altair as alt

select_year = alt.selection_point(
    name="Year",
    fields=["iteration"],
    bind=alt.binding_range(min=1900, max=2000, step=10, name="Year"),
    value={"iteration": 2000},
)

[mattijn]

Thanks for raising the issue! I can reproduce the error you are facing. The correct syntax that you should use in this situation is the following:

select_year = alt.selection_point(
    name="Year",
    fields=["iteration"],
    bind=alt.binding_range(min=1900, max=2000, step=10, name="Year"),
    value=2000
)

So instead of value={"iteration": 2000} you should use just value=2000. This is a change compare to the previous init argument. I'm not sure if this change is properly documented somewhere in the release notes when this was introduced.

[mattijn]

Ah, I see that you actually refer to this example in the documentation: https://altair-viz.github.io/gallery/us_population_over_time.html. That should be updated!

[jpn--]

Thanks @mattijn. Now knowing the correct syntax, I've opened a PR to fix the docs in the places where the outdated syntax was used.