How to do waffle charts in python? (square piechart)

Question

Something like this:

There is a very good package to do it in R. In python, the best that I could figure out is this, using the squarify package (inspi

Answer 1

I've put together a working example, below, which I think meets your needs. Some work is needed to fully generalize the approach, but I think you'll find that it's a good start. The trick was to use matshow() to solve your non-square problem, and to build a custom legend to easily account for categorical values.

import numpy as np
import pandas as pd
import matplotlib as mpl
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches

# Let's make a default data frame with catagories and values.
df = pd.DataFrame({ 'catagories': ['cat1', 'cat2', 'cat3', 'cat4'], 
                    'values': [84911, 14414, 10062, 8565] })
# Now, we define a desired height and width.
waffle_plot_width = 20
waffle_plot_height = 7

classes = df['catagories']
values = df['values']

def waffle_plot(classes, values, height, width, colormap):

    # Compute the portion of the total assigned to each class.
    class_portion = [float(v)/sum(values) for v in values]

    # Compute the number of tiles for each catagories.
    total_tiles = width * height
    tiles_per_class = [round(p*total_tiles) for p in class_portion]

    # Make a dummy matrix for use in plotting.
    plot_matrix = np.zeros((height, width))

    # Popoulate the dummy matrix with integer values.
    class_index = 0
    tile_index = 0

    # Iterate over each tile.
    for col in range(waffle_plot_width):
        for row in range(height):
            tile_index += 1

            # If the number of tiles populated is sufficient for this class...
            if tile_index > sum(tiles_per_class[0:class_index]):

                # ...increment to the next class.
                class_index += 1       

            # Set the class value to an integer, which increases with class.
            plot_matrix[row, col] = class_index

    # Create a new figure.
    fig = plt.figure()

    # Using matshow solves your "non-square" problem. 
    plt.matshow(plot_matrix, cmap=colormap)
    plt.colorbar()

    # Get the axis.
    ax = plt.gca()

    # Minor ticks
    ax.set_xticks(np.arange(-.5, (width), 1), minor=True);
    ax.set_yticks(np.arange(-.5, (height), 1), minor=True);

    # Gridlines based on minor ticks
    ax.grid(which='minor', color='w', linestyle='-', linewidth=2)

    # Manually constructing a legend solves your "catagorical" problem.
    legend_handles = []
    for i, c in enumerate(classes):
        lable_str = c + " (" + str(values[i]) + ")"
        color_val = colormap(float(i+1)/len(classes))
        legend_handles.append(mpatches.Patch(color=color_val, label=lable_str))

    # Add the legend. Still a bit of work to do here, to perfect centering.
    plt.legend(handles=legend_handles, loc=1, ncol=len(classes),
               bbox_to_anchor=(0., -0.1, 0.95, .10))

    plt.xticks([])
    plt.yticks([])

# Call the plotting function.
waffle_plot(classes, values, waffle_plot_height, waffle_plot_width,
            plt.cm.coolwarm)

Below is an example of the output this script produced. As you can see, it works fairly well for me, and meets all of your stated needs. Just let me know if it gives you any trouble. Enjoy!