How to Plot Two Histograms Together in Matplotlib

1. Two Histograms without Overlapping Bars
2. Two Histograms with Overlapping Bars

We could plot two histograms in one figure at the same time. Below shows methods to create the two histograms with and without overlapping bars.

Two Histograms without Overlapping Bars

Working Example Codes:

import numpy as np
import matplotlib.pyplot as plt

a = np.random.normal(0, 3, 3000)
b = np.random.normal(2, 4, 2000)

bins = np.linspace(-10, 10, 20)

plt.hist([a, b], bins, label=['a', 'b'])
plt.legend(loc='upper left')
plt.show()

Two Histograms with Overlapping Bars

Working Example Codes:

import numpy as np
import matplotlib.pyplot as plt

a = np.random.normal(0, 3, 1000)
b = np.random.normal(2, 4, 900)

bins = np.linspace(-10, 10, 50)

plt.hist(a, bins, alpha = 0.5, label='a')
plt.hist(b, bins, alpha = 0.5, label='b')
plt.legend(loc='upper left')

plt.show()

When we call plt.hist twice to plot the histograms individually, the two histograms will have the overlapped bars as you could see above.

The alpha property specifies the transparency of the plot. 0.0 is transparent and 1.0 is opaque.

When alpha is set to be 0.5 for both histograms, the overlapped area shows the combined color. But if alpha is 0.0, the default value, overlapped bar only shows the color of the higher value among two histograms and the other color is hidden, as shown below.