CODEWITHSUNDEEP
altair
MrSteve
MrSteve

Reputation: 499

How can I select data for a chart based on a dropdown?

I have a dataframe for which I want to sub-select a set of rows based on a dropdown. So Given the following code:

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

cars = pd.melt(data.cars(), ['Horsepower', 'Origin', 'Name', 'Year'])
cars.head()

select_box = alt.binding_select(options=list(cars['variable'].unique()))
selection = alt.selection_single(name='d_axis', fields=['variable'], bind=select_box)

alt.Chart(cars).mark_point().encode(
    x='Horsepower',
    y='value',
    color='Origin',
    tooltip='Name'
).add_selection(
    selection
).transform_filter(
    selection
)

Instead of changing the X values, I want to only select cars where Origin is 'USA'.
So in effect something where

alt.Chart(cars).mark_point().encode(

becomes:

alt.Chart(cars[cars['Origin'] == selection]).mark_point().encode(

Thanks, Stephen

Upvotes: 2

Views: 1087

Answers (1)

jakevdp
jakevdp

Reputation: 86433

You can tie the selection to the field you want to filter:

import altair as alt
from vega_datasets import data

cars = data.cars()

select_box = alt.binding_select(options=list(cars['Origin'].unique()))
selection = alt.selection_single(fields=['Origin'], bind=select_box)

alt.Chart(cars).mark_point().encode(
    x='Horsepower',
    y='Miles_per_Gallon'
).add_selection(
    selection
).transform_filter(
    selection
)

enter image description here

Upvotes: 2

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