Set background color to matplotlib chart

Question

I'm generating an orderbook chart using Matplotlib, the chart is generated but i'm having an hard time figuring how to set a background color to it. On the chart, i'm plotting 2 orderbooks for every side, to do this i'm using a simple loop on my data:

fig = plt.figure(facecolor='#131722',dpi=135, figsize=(5, 3))
ax1 = plt.subplot2grid((2,1), (0,0), rowspan=6, colspan=4, facecolor='#131722')


Colors = [['#2BBB2B', '#FF0000'], ['#09ff00', '#ff8c00']]

for x in List:

    Index = List.index(x)

    print(Index)

    rate_buy = []
    total_buy = []
    rate_sell = []
    total_sell = []

    for y in x['data']['asks']:
        rate_sell.append(y[0])
        total_sell.append(y[1])

    for y in x['data']['bids']:
        rate_buy.append(y[0])
        total_buy.append(y[1])

    rBuys = pd.DataFrame({'buy': rate_buy})
    rSells = pd.DataFrame({'sell': rate_sell})
    tBuys = pd.DataFrame({'total': total_buy})
    tSells = pd.DataFrame({'total': total_sell})

    plt.plot(rBuys.buy, tBuys.total, color=Colors[Index][0], linewidth=0.9, alpha=0.9)
    plt.plot(rSells.sell, tSells.total, color=Colors[Index][1],alpha=0.3, linewidth=0.9)

The output is the following:

So basically, what i want to do, is set the area INSIDE the chart with the same color of the value Color. How can i do that?

Zephyr · Accepted Answer · 2020-06-04 21:05:32Z

You can use a np.vstack function to create an array of x and y coordinates for the area, then plot it trhough the Polygon function, as this:

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.patches import Polygon

x = np.linspace(0, 10, 11)
y1 = np.array([4, 5, 6, 9, 11, 7, 6, 2, 4, 4, 5])
y2 = np.array([4, 3, 2, 1, 1, 6, 5, 7, 7, 6, 5])

# here I concatenate the x and y arrays for the border of the area
# two times x for back and forth
# y1 and y2 for the top and bottom part of the area
area = np.vstack((np.concatenate((x, x[::-1])),
                  np.concatenate((y1, y2[::-1])))).T

fig, ax = plt.subplots(1, 1, figsize = (8, 8))

ax.plot(x, y1, 'r-', lw = 2, label = 'y1')
ax.plot(x, y2, 'b-', lw = 2, label = 'y2')

# here I add the area to the plot
ax.add_patch(Polygon(area, facecolor = 'g', alpha = 0.5))

ax.grid()
ax.legend()

plt.show()

which gives you this:

In your chart there are 4 curves, which I call light-green, dark-green, red and brown. If you want to color the part of the graph between light-green and dark-green you should fill in the vstack vector in the following way:

area_1 = np.vstack((np.concatenate((x_of_light-green, x_of_dark-green[::-1])),
                    np.concatenate((y_of_light-green, y_of_dark-green[::-1])))).T

The [::-1] after the arrays is necessary in order to reverse the order of the element: with the x_of_light-green and y_of_light-green you define the forth (the bottom border of the colored area), while with the x_of_dark-green[::-1] and y_of_dark-green[::-1] you define the back (the top border of the colored area).

While for the region between the red and brown curves:

area_2 = np.vstack((np.concatenate((x_of_red, x_of_brown[::-1])),
                    np.concatenate((y_of_red, y_of_brown[::-1])))).T

Replace x_of_... and y_of_... with the data of the dataframe you are considering.
Once you have defined these area, you can add them to your graph with the ax1.add_path(Polygon(area_1)) and ax1.add_path(Polygon(area_2)).

Try to replace the x_of_... and y_of_... with the abscissas and ordinates you used for you graph. Another, simpler way is to use the method ax.fill_between(x, y2, y1, facecolor = 'green', alpha = 0.5)

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