.. 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_fill_between_demo.py: ============================== Filling the area between lines ============================== This example shows how to use `~.axes.Axes.fill_between` to color the area between two lines. .. code-block:: default import matplotlib.pyplot as plt import numpy as np Basic usage ----------- The parameters *y1* and *y2* can be scalars, indicating a horizontal boundary at the given y-values. If only *y1* is given, *y2* defaults to 0. .. code-block:: default x = np.arange(0.0, 2, 0.01) y1 = np.sin(2 * np.pi * x) y2 = 0.8 * np.sin(4 * np.pi * x) fig, (ax1, ax2, ax3) = plt.subplots(3, 1, sharex=True, figsize=(6, 6)) ax1.fill_between(x, y1) ax1.set_title('fill between y1 and 0') ax2.fill_between(x, y1, 1) ax2.set_title('fill between y1 and 1') ax3.fill_between(x, y1, y2) ax3.set_title('fill between y1 and y2') ax3.set_xlabel('x') fig.tight_layout() .. image:: /gallery/lines_bars_and_markers/images/sphx_glr_fill_between_demo_001.png :alt: fill between y1 and 0, fill between y1 and 1, fill between y1 and y2 :class: sphx-glr-single-img Example: Confidence bands ------------------------- A common application for `~.axes.Axes.fill_between` is the indication of confidence bands. `~.axes.Axes.fill_between` uses the colors of the color cycle as the fill color. These may be a bit strong when applied to fill areas. It is therefore often a good practice to lighten the color by making the area semi-transparent using *alpha*. .. code-block:: default N = 21 x = np.linspace(0, 10, 11) y = [3.9, 4.4, 10.8, 10.3, 11.2, 13.1, 14.1, 9.9, 13.9, 15.1, 12.5] # fit a linear curve an estimate its y-values and their error. a, b = np.polyfit(x, y, deg=1) y_est = a * x + b y_err = x.std() * np.sqrt(1/len(x) + (x - x.mean())**2 / np.sum((x - x.mean())**2)) fig, ax = plt.subplots() ax.plot(x, y_est, '-') ax.fill_between(x, y_est - y_err, y_est + y_err, alpha=0.2) ax.plot(x, y, 'o', color='tab:brown') .. image:: /gallery/lines_bars_and_markers/images/sphx_glr_fill_between_demo_002.png :alt: fill between demo :class: sphx-glr-single-img .. rst-class:: sphx-glr-script-out Out: .. code-block:: none [] Selectively filling horizontal regions -------------------------------------- The parameter *where* allows to specify the x-ranges to fill. It's a boolean array with the same size as *x*. Only x-ranges of contiguous *True* sequences are filled. As a result the range between neighboring *True* and *False* values is never filled. This often undesired when the data points should represent a contiguous quantity. It is therefore recommended to set ``interpolate=True`` unless the x-distance of the data points is fine enough so that the above effect is not noticeable. Interpolation approximates the actual x position at which the *where* condition will change and extends the filling up to there. .. code-block:: default x = np.array([0, 1, 2, 3]) y1 = np.array([0.8, 0.8, 0.2, 0.2]) y2 = np.array([0, 0, 1, 1]) fig, (ax1, ax2) = plt.subplots(2, 1, sharex=True) ax1.set_title('interpolation=False') ax1.plot(x, y1, 'o--') ax1.plot(x, y2, 'o--') ax1.fill_between(x, y1, y2, where=(y1 > y2), color='C0', alpha=0.3) ax1.fill_between(x, y1, y2, where=(y1 < y2), color='C1', alpha=0.3) ax2.set_title('interpolation=True') ax2.plot(x, y1, 'o--') ax2.plot(x, y2, 'o--') ax2.fill_between(x, y1, y2, where=(y1 > y2), color='C0', alpha=0.3, interpolate=True) ax2.fill_between(x, y1, y2, where=(y1 <= y2), color='C1', alpha=0.3, interpolate=True) fig.tight_layout() .. image:: /gallery/lines_bars_and_markers/images/sphx_glr_fill_between_demo_003.png :alt: interpolation=False, interpolation=True :class: sphx-glr-single-img .. note:: Similar gaps will occur if *y1* or *y2* are masked arrays. Since missing values cannot be approximated, *interpolate* has no effect in this case. The gaps around masked values can only be reduced by adding more data points close to the masked values. Selectively marking horizontal regions across the whole Axes ------------------------------------------------------------ The same selection mechanism can be applied to fill the full vertical height of the axes. To be independent of y-limits, we add a transform that interprets the x-values in data coorindates and the y-values in axes coordinates. The following example marks the regions in which the y-data are above a given threshold. .. code-block:: default fig, ax = plt.subplots() x = np.arange(0, 4 * np.pi, 0.01) y = np.sin(x) ax.plot(x, y, color='black') threshold = 0.75 ax.axhline(threshold, color='green', lw=2, alpha=0.7) ax.fill_between(x, 0, 1, where=y > threshold, color='green', alpha=0.5, transform=ax.get_xaxis_transform()) .. image:: /gallery/lines_bars_and_markers/images/sphx_glr_fill_between_demo_004.png :alt: fill between demo :class: sphx-glr-single-img .. rst-class:: sphx-glr-script-out Out: .. code-block:: none .. admonition:: References The use of the following functions, methods, classes and modules is shown in this example: - `matplotlib.axes.Axes.fill_between` / `matplotlib.pyplot.fill_between` - `matplotlib.axes.Axes.get_xaxis_transform` .. rst-class:: sphx-glr-timing **Total running time of the script:** ( 0 minutes 1.495 seconds) .. _sphx_glr_download_gallery_lines_bars_and_markers_fill_between_demo.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: fill_between_demo.py ` .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: fill_between_demo.ipynb ` .. only:: html .. rst-class:: sphx-glr-signature Keywords: matplotlib code example, codex, python plot, pyplot `Gallery generated by Sphinx-Gallery `_