.. note::
    :class: sphx-glr-download-link-note

    Click :ref:`here <sphx_glr_download_gallery_pie_and_polar_charts_nested_pie.py>` to download the full example code
.. rst-class:: sphx-glr-example-title

.. _sphx_glr_gallery_pie_and_polar_charts_nested_pie.py:


=================
Nested pie charts
=================

The following examples show two ways to build a nested pie chart
in Matplotlib. Such charts are often referred to as donut charts.




.. code-block:: python


    import matplotlib.pyplot as plt
    import numpy as np







The most straightforward way to build a pie chart is to use the
:meth:`pie method <matplotlib.axes.Axes.pie>`

In this case, pie takes values corresponding to counts in a group.
We'll first generate some fake data, corresponding to three groups.
In the inner circle, we'll treat each number as belonging to its
own group. In the outer circle, we'll plot them as members of their
original 3 groups.

The effect of the donut shape is achieved by setting a `width` to
the pie's wedges through the `wedgeprops` argument.



.. code-block:: python



    fig, ax = plt.subplots()

    size = 0.3
    vals = np.array([[60., 32.], [37., 40.], [29., 10.]])

    cmap = plt.get_cmap("tab20c")
    outer_colors = cmap(np.arange(3)*4)
    inner_colors = cmap(np.array([1, 2, 5, 6, 9, 10]))

    ax.pie(vals.sum(axis=1), radius=1, colors=outer_colors,
           wedgeprops=dict(width=size, edgecolor='w'))

    ax.pie(vals.flatten(), radius=1-size, colors=inner_colors,
           wedgeprops=dict(width=size, edgecolor='w'))

    ax.set(aspect="equal", title='Pie plot with `ax.pie`')
    plt.show()




.. image:: /gallery/pie_and_polar_charts/images/sphx_glr_nested_pie_001.png
    :class: sphx-glr-single-img




However, you can accomplish the same output by using a bar plot on
axes with a polar coordinate system. This may give more flexibility on
the exact design of the plot.

In this case, we need to map x-values of the bar chart onto radians of
a circle. The cumulative sum of the values are used as the edges
of the bars.



.. code-block:: python


    fig, ax = plt.subplots(subplot_kw=dict(polar=True))

    size = 0.3
    vals = np.array([[60., 32.], [37., 40.], [29., 10.]])
    #normalize vals to 2 pi
    valsnorm = vals/np.sum(vals)*2*np.pi
    #obtain the ordinates of the bar edges
    valsleft = np.cumsum(np.append(0, valsnorm.flatten()[:-1])).reshape(vals.shape)

    cmap = plt.get_cmap("tab20c")
    outer_colors = cmap(np.arange(3)*4)
    inner_colors = cmap(np.array([1, 2, 5, 6, 9, 10]))

    ax.bar(x=valsleft[:, 0],
           width=valsnorm.sum(axis=1), bottom=1-size, height=size,
           color=outer_colors, edgecolor='w', linewidth=1, align="edge")

    ax.bar(x=valsleft.flatten(),
           width=valsnorm.flatten(), bottom=1-2*size, height=size,
           color=inner_colors, edgecolor='w', linewidth=1, align="edge")

    ax.set(title="Pie plot with `ax.bar` and polar coordinates")
    ax.set_axis_off()
    plt.show()




.. image:: /gallery/pie_and_polar_charts/images/sphx_glr_nested_pie_002.png
    :class: sphx-glr-single-img




------------

References
""""""""""

The use of the following functions, methods, classes and modules is shown
in this example:



.. code-block:: python


    import matplotlib
    matplotlib.axes.Axes.pie
    matplotlib.pyplot.pie
    matplotlib.axes.Axes.bar
    matplotlib.pyplot.bar
    matplotlib.projections.polar
    matplotlib.axes.Axes.set
    matplotlib.axes.Axes.set_axis_off







.. _sphx_glr_download_gallery_pie_and_polar_charts_nested_pie.py:


.. only :: html

 .. container:: sphx-glr-footer
    :class: sphx-glr-footer-example



  .. container:: sphx-glr-download

     :download:`Download Python source code: nested_pie.py <nested_pie.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: nested_pie.ipynb <nested_pie.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    Keywords: matplotlib code example, codex, python plot, pyplot
    `Gallery generated by Sphinx-Gallery
    <https://sphinx-gallery.readthedocs.io>`_
