.. only:: html .. note:: :class: sphx-glr-download-link-note Click :ref:`here ` to download the full example code .. rst-class:: sphx-glr-example-title .. _sphx_glr_gallery_lines_bars_and_markers_scatter_with_legend.py: =========================== Scatter plots 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. .. code-block:: default import numpy as np np.random.seed(19680801) import matplotlib.pyplot as plt 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:: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_001.png :alt: scatter with legend :class: sphx-glr-single-img .. _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`. .. code-block:: default 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:: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_002.png :alt: scatter with legend :class: sphx-glr-single-img 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. .. code-block:: default 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:: /gallery/lines_bars_and_markers/images/sphx_glr_scatter_with_legend_003.png :alt: scatter with legend :class: sphx-glr-single-img ------------ References """""""""" The usage of the following functions and methods is shown in this example: .. code-block:: default import matplotlib matplotlib.axes.Axes.scatter matplotlib.pyplot.scatter matplotlib.axes.Axes.legend matplotlib.pyplot.legend matplotlib.collections.PathCollection.legend_elements .. rst-class:: sphx-glr-script-out Out: .. code-block:: none .. rst-class:: sphx-glr-timing **Total running time of the script:** ( 0 minutes 1.492 seconds) .. _sphx_glr_download_gallery_lines_bars_and_markers_scatter_with_legend.py: .. only :: html .. container:: sphx-glr-footer :class: sphx-glr-footer-example .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: scatter_with_legend.py ` .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: scatter_with_legend.ipynb ` .. only:: html .. rst-class:: sphx-glr-signature Keywords: matplotlib code example, codex, python plot, pyplot `Gallery generated by Sphinx-Gallery `_