Add blank dropdown option that doesn't filter

[ZaxR]

I have a chart with a dropdown selector, and the selection is responsible for filtering the data displayed in the chart. I'm trying to add a "blank" option to the binding_select that will result in no filtering (i.e. "display all data"). Is there an easy way to do that?

I was looking at alt.condition and filter predicates, but wasn't able to figure it out. I was playing with the following example, where i'd want an "All" selection in the binding_select:

import altair as alt
from vega_datasets import data


cars = data.cars.url

input_dropdown = alt.binding_select(options=['All', 'Europe','Japan','USA'])
selection = alt.selection_single(fields=['Origin'],
                                 bind=input_dropdown,
                                 name='Country of ',
                                 init={'Origin': 'Europe'})
color = alt.condition(selection,
                    alt.Color('Origin:N', legend=None),
                    alt.value('lightgray'))

alt.Chart(cars).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color='Origin:N',
    tooltip='Name:N'
).add_selection(
    selection
).transform_filter(
    selection
   # Looking for something like <no filter> if selection == 'All' else selection
)

Thanks for the library and for the help!

[jakevdp]

It's a bit hacky, but this works:

alt.Chart(cars).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color='Origin:N',
    tooltip='Name:N'
).add_selection(
    selection
).transform_filter(
   f"({selection.Origin}[0] == 'All') || ({selection.Origin}[0] == datum.Origin)"
)

It would be nice to update the altair expression syntax so that this condition could be written like this instead:

(selection.Origin[0] == 'All') | (selection.Origin[0] == alt.datum.Origin)

[ZaxR]

Thanks for the quick response.

That syntax doesn't seem to be working for me - am I doing something wrong? Here's what I get when I try (w/ Altair 4.1.0, vega 3.2.0):

Text for reproducability:

import altair as alt
from vega_datasets import data

cars = data.cars.url

input_dropdown = alt.binding_select(options=['All','Europe','Japan','USA'])
selection = alt.selection_single(fields=['Origin'],
                                 bind=input_dropdown,
                                 name='Country of ',
                                 init={'Origin': 'Europe'})

alt.Chart(cars).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color='Origin:N',
    tooltip='Name:N'
).add_selection(
    selection
).transform_filter(
   f"({selection.Origin}[0] == 'All') || ({selection.Origin}[0] == datum.Origin)"
)

[ZaxR]

Looks like adding None as an option works, and the associated label is null (idea came from https://vega.github.io/vega-lite/docs/bind.html#input-element-binding). Not ideal, but does the right thing it looks like:

[jakevdp]

Oh, sorry, you have to use selection names that are valid identifiers. Try this:

import altair as alt
from vega_datasets import data

cars = data.cars.url

input_dropdown = alt.binding_select(options=['All','Europe','Japan','USA'], name="Country")
selection = alt.selection_single(fields=['Origin'],
                                 bind=input_dropdown,
                                 init={'Origin': 'Europe'})

alt.Chart(cars).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color='Origin:N',
    tooltip='Name:N'
).add_selection(
    selection
).transform_filter(
   f"({selection.Origin}[0] == 'All') || ({selection.Origin}[0] == datum.Origin)"
)

[ZaxR]

Awesome - thanks!

[joelostblom]

@ZaxR I am going through Altair issues to find those that have been resolved and can be closed. It looks to me like this issue has been solved so I am closing it, but please feel free to reopen and add a comment if there is something you don't think is resolved yet.