Version 3.1.2
matplotlib

Discrete distribution as horizontal bar chart

Stacked bar charts can be used to visualize discrete distributions.

This example visualizes the result of a survey in which people could rate their agreement to questions on a five-element scale.

The horizontal stacking is achieved by calling barh() for each category and passing the starting point as the cumulative sum of the already drawn bars via the parameter left.

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Discrete distribution as horizontal bar chart
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Stacked bar charts can be used to visualize discrete distributions.

This example visualizes the result of a survey in which people could rate
their agreement to questions on a five-element scale.

The horizontal stacking is achieved by calling `~.Axes.barh()` for each
category and passing the starting point as the cumulative sum of the
already drawn bars via the parameter ``left``.
"""

import numpy as np
import matplotlib.pyplot as plt


category_names = ['Strongly disagree', 'Disagree',
                  'Neither agree nor disagree', 'Agree', 'Strongly agree']
results = {
    'Question 1': [10, 15, 17, 32, 26],
    'Question 2': [26, 22, 29, 10, 13],
    'Question 3': [35, 37, 7, 2, 19],
    'Question 4': [32, 11, 9, 15, 33],
    'Question 5': [21, 29, 5, 5, 40],
    'Question 6': [8, 19, 5, 30, 38]
}


def survey(results, category_names):
    """
    Parameters
    ----------
    results : dict
        A mapping from question labels to a list of answers per category.
        It is assumed all lists contain the same number of entries and that
        it matches the length of *category_names*.
    category_names : list of str
        The category labels.
    """
    labels = list(results.keys())
    data = np.array(list(results.values()))
    data_cum = data.cumsum(axis=1)
    category_colors = plt.get_cmap('RdYlGn')(
        np.linspace(0.15, 0.85, data.shape[1]))

    fig, ax = plt.subplots(figsize=(9.2, 5))
    ax.invert_yaxis()
    ax.xaxis.set_visible(False)
    ax.set_xlim(0, np.sum(data, axis=1).max())

    for i, (colname, color) in enumerate(zip(category_names, category_colors)):
        widths = data[:, i]
        starts = data_cum[:, i] - widths
        ax.barh(labels, widths, left=starts, height=0.5,
                label=colname, color=color)
        xcenters = starts + widths / 2

        r, g, b, _ = color
        text_color = 'white' if r * g * b < 0.5 else 'darkgrey'
        for y, (x, c) in enumerate(zip(xcenters, widths)):
            ax.text(x, y, str(int(c)), ha='center', va='center',
                    color=text_color)
    ax.legend(ncol=len(category_names), bbox_to_anchor=(0, 1),
              loc='lower left', fontsize='small')

    return fig, ax


survey(results, category_names)
plt.show()
Traceback (most recent call last):
  File "/build/matplotlib-mO9dyQ/matplotlib-3.1.2/examples/lines_bars_and_markers/horizontal_barchart_distribution.py", line 1
    =============================================
    ^
SyntaxError: invalid syntax

References

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

import matplotlib
matplotlib.axes.Axes.barh
matplotlib.pyplot.barh
matplotlib.axes.Axes.text
matplotlib.pyplot.text
matplotlib.axes.Axes.legend
matplotlib.pyplot.legend

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