.. This document is auto-generated by the altair-gallery extension. Do not modify directly.

.. _gallery_us_population_pyramid_over_time:


US Population Pyramid Over Time
===============================
A population pyramid shows the distribution of age groups within a population.
It uses a slider widget that is bound to the year to visualize the age
distribution over time.


.. altair-plot::
    :code-below:

    
    import altair as alt
    from altair.expr import datum, if_
    from vega_datasets import data

    pop = data.population.url

    slider = alt.binding_range(min=1850, max=2000, step=10)
    select_year = alt.selection_single(name='year', fields=['year'], bind=slider)

    base = alt.Chart(pop).add_selection(
        select_year
    ).transform_filter(
        select_year
    ).transform_calculate(
        gender=if_(datum.sex == 1, 'Male', 'Female')
    )

    title = alt.Axis(title='population')
    color_scale = alt.Scale(domain=['Male', 'Female'],
                            range=['#1f77b4', '#e377c2'])

    left = base.transform_filter(
        datum.gender == 'Female'
    ).encode(
        y=alt.X('age:O', axis=None),
        x=alt.X('sum(people):Q', axis=title, sort=alt.SortOrder('descending')),
        color=alt.Color('gender:N', scale=color_scale, legend=None)
    ).mark_bar().properties(title='Female')

    middle = base.encode(
        y=alt.X('age:O', axis=None),
        text=alt.Text('age:Q'),
    ).mark_text().properties(width=20)

    right = base.transform_filter(
        datum.gender == 'Male'
    ).encode(
        y=alt.X('age:O', axis=None),
        x=alt.X('sum(people):Q', axis=title),
        color=alt.Color('gender:N', scale=color_scale, legend=None)
    ).mark_bar().properties(title='Male')

    left | middle | right

.. toctree::
   :hidden: