
.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "gallery/lines_bars_and_markers/scatter_with_legend.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. meta::
        :keywords: codex

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

        :ref:`Go to the end <sphx_glr_download_gallery_lines_bars_and_markers_scatter_with_legend.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_gallery_lines_bars_and_markers_scatter_with_legend.py:


==========================
Scatter plot with a legend
==========================

To create a scatter plot with a legend one may use a loop and create one
`~.Axes.scatter` plot per item to appear in the legend and set the ``label``
accordingly.

The following also demonstrates how transparency of the markers
can be adjusted by giving ``alpha`` a value between 0 and 1.

.. GENERATED FROM PYTHON SOURCE LINES 13-34

.. code-block:: Python


    import matplotlib.pyplot as plt
    import numpy as np

    np.random.seed(19680801)


    fig, ax = plt.subplots()
    for color in ['tab:blue', 'tab:orange', 'tab:green']:
        n = 750
        x, y = np.random.rand(2, n)
        scale = 200.0 * np.random.rand(n)
        ax.scatter(x, y, c=color, s=scale, label=color,
                   alpha=0.3, edgecolors='none')

    ax.legend()
    ax.grid(True)

    plt.show()





.. image-sg:: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_001.png
   :alt: scatter with legend
   :srcset: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_001.png, /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_001_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 35-44

.. _automatedlegendcreation:

Automated legend creation
-------------------------

Another option for creating a legend for a scatter is to use the
`.PathCollection.legend_elements` method.  It will automatically try to
determine a useful number of legend entries to be shown and return a tuple of
handles and labels. Those can be passed to the call to `~.axes.Axes.legend`.

.. GENERATED FROM PYTHON SOURCE LINES 44-67

.. code-block:: Python



    N = 45
    x, y = np.random.rand(2, N)
    c = np.random.randint(1, 5, size=N)
    s = np.random.randint(10, 220, size=N)

    fig, ax = plt.subplots()

    scatter = ax.scatter(x, y, c=c, s=s)

    # produce a legend with the unique colors from the scatter
    legend1 = ax.legend(*scatter.legend_elements(),
                        loc="lower left", title="Classes")
    ax.add_artist(legend1)

    # produce a legend with a cross-section of sizes from the scatter
    handles, labels = scatter.legend_elements(prop="sizes", alpha=0.6)
    legend2 = ax.legend(handles, labels, loc="upper right", title="Sizes")

    plt.show()





.. image-sg:: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_002.png
   :alt: scatter with legend
   :srcset: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_002.png, /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_002_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 68-71

Further arguments to the `.PathCollection.legend_elements` method
can be used to steer how many legend entries are to be created and how they
should be labeled. The following shows how to use some of them.

.. GENERATED FROM PYTHON SOURCE LINES 71-102

.. code-block:: Python


    volume = np.random.rayleigh(27, size=40)
    amount = np.random.poisson(10, size=40)
    ranking = np.random.normal(size=40)
    price = np.random.uniform(1, 10, size=40)

    fig, ax = plt.subplots()

    # Because the price is much too small when being provided as size for ``s``,
    # we normalize it to some useful point sizes, s=0.3*(price*3)**2
    scatter = ax.scatter(volume, amount, c=ranking, s=0.3*(price*3)**2,
                         vmin=-3, vmax=3, cmap="Spectral")

    # Produce a legend for the ranking (colors). Even though there are 40 different
    # rankings, we only want to show 5 of them in the legend.
    legend1 = ax.legend(*scatter.legend_elements(num=5),
                        loc="upper left", title="Ranking")
    ax.add_artist(legend1)

    # Produce a legend for the price (sizes). Because we want to show the prices
    # in dollars, we use the *func* argument to supply the inverse of the function
    # used to calculate the sizes from above. The *fmt* ensures to show the price
    # in dollars. Note how we target at 5 elements here, but obtain only 4 in the
    # created legend due to the automatic round prices that are chosen for us.
    kw = dict(prop="sizes", num=5, color=scatter.cmap(0.7), fmt="$ {x:.2f}",
              func=lambda s: np.sqrt(s/.3)/3)
    legend2 = ax.legend(*scatter.legend_elements(**kw),
                        loc="lower right", title="Price")

    plt.show()




.. image-sg:: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_003.png
   :alt: scatter with legend
   :srcset: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_003.png, /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_003_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 103-117

.. admonition:: References

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

   - `matplotlib.axes.Axes.scatter` / `matplotlib.pyplot.scatter`
   - `matplotlib.axes.Axes.legend` / `matplotlib.pyplot.legend`
   - `matplotlib.collections.PathCollection.legend_elements`

.. tags::

   component: legend
   plot-type: scatter
   level: intermediate


.. _sphx_glr_download_gallery_lines_bars_and_markers_scatter_with_legend.py:

.. only:: html

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

    .. container:: sphx-glr-download sphx-glr-download-jupyter

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

    .. container:: sphx-glr-download sphx-glr-download-python

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

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: scatter_with_legend.zip <scatter_with_legend.zip>`


.. only:: html

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

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_
