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.

Asked By: GrieferDen

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Source

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)

Answered By: joelostblom

Answer 2

More general solution can be drawn from this article.

from vega_datasets import data
import altair as alt

def table(df):
    return (
        alt.Chart(df.reset_index())
        .mark_text()
        .transform_fold(df.columns.tolist())
        .encode(
            alt.X(
                "key",
                type="nominal",
                axis=alt.Axis(
                    # flip x labels upside down
                    orient="top",
                    # put x labels into horizontal direction
                    labelAngle=0,
                    title=None,
                    ticks=False
                ),
                scale=alt.Scale(padding=10),
                sort=None,
            ),
            alt.Y("index", type="ordinal", axis=None),
            alt.Text("value", type="nominal"),
        )
    )

source = data.cars()

# display only 15 rows
table(source[:15]).properties(width=1500)

Answered By: Gompro

Python Altair Generate a table on selection

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