Python Altair Generate a table on selection

Question

I have a histogram with a bunch of binned data and I was wondering if it would be possible to say generate a table if I select a bar from the histogram and it would display the data as it is in the original dataframe.

Answer 1

You can create the appearance of a table using mark_text. Here is an example based on this page in the docs:

import altair as alt
from vega_datasets import data

source = data.cars()

# Brush for selection
brush = alt.selection(type='interval')

# Scatter Plot
points = alt.Chart(source).mark_point().encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color=alt.condition(brush, alt.value('steelblue'), alt.value('grey'))
).add_selection(brush)

# Base chart for data tables
ranked_text = alt.Chart(source).mark_text(align='right').encode(
    y=alt.Y('row_number:O',axis=None)
).transform_filter(
    brush
).transform_window(
    row_number='row_number()'
).transform_filter(
    'datum.row_number < 15'
)

# Data Tables
horsepower = ranked_text.encode(text='Horsepower:N').properties(title=alt.TitleParams(text='Horsepower', align='right'))
mpg = ranked_text.encode(text='Miles_per_Gallon:N').properties(title=alt.TitleParams(text='MPG', align='right'))
origin = ranked_text.encode(text='Origin:N').properties(title=alt.TitleParams(text='Origin', align='right'))
text = alt.hconcat(horsepower, mpg, origin) # Combine data tables

# Build chart
alt.hconcat(
    points,
    text
).resolve_legend(
    color="independent"
).configure_view(strokeWidth=0)

For a histogram, things are slightly different due to current limitation in Vega-Lite and you need to create a second filtered layer to visually show the selection in the histogram.

import altair as alt
from vega_datasets import data


source = data.cars()

# Brush for selection
brush = alt.selection(type='single', encodings=['x'])

# Histogram base
hist_base = alt.Chart(source).mark_bar(color='grey').encode(
    x=alt.X('Horsepower:Q', bin=True),
    y='count()',
).add_selection(brush)

# Histogram selection
hist_selection = alt.Chart(source).mark_bar().encode(
    x=alt.X('Horsepower:Q', bin=True),
    y='count()',
).transform_filter(brush)

# Base chart for data tables
ranked_text = alt.Chart(source).mark_text(align='right').encode(
    y=alt.Y('row_number:O',axis=None)
).transform_filter(
    brush
).transform_window(
    row_number='row_number()'
).transform_filter(
    'datum.row_number < 15'
)

# Data Tables
horsepower = ranked_text.encode(text='Horsepower:N').properties(title=alt.TitleParams(text='Horsepower', align='right'))
mpg = ranked_text.encode(text='Miles_per_Gallon:N').properties(title=alt.TitleParams(text='MPG', align='right'))
origin = ranked_text.encode(text='Origin:N').properties(title=alt.TitleParams(text='Origin', align='right'))
text = alt.hconcat(horsepower, mpg, origin) # Combine data tables

# Build chart
alt.hconcat(
    hist_base+hist_selection,
    text
).resolve_legend(
    color="independent"
).configure_view(strokeWidth=0)