如何使用 Matplotlib 在图中添加多个直方图？

Question

I'm using matplotlib to plot many histograms in one plot successfully:

import matplotlib.pyplot as plt
import numpy as np

np.random.seed(1)

for i in range(0, 6):
    data = np.random.normal(size=1000)
    plt.hist(data, bins=30, alpha = 0.5)
plt.show()

However, I wish to export this plot in a pdf, using PdfPages. I want to add each histogram in a separate page, which I successfully do like this:

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.backends.backend_pdf import PdfPages

np.random.seed(1)

fig = []
with PdfPages("exported_data.pdf") as pdf:
    for i in range(0, 6):
        data = np.random.normal(size=1000)
        fig.append(plt.hist(data, bins=30, alpha = 0.5))
        pdf.savefig(fig[i])
        plt.close()

But I want another, 7th page with all the plots in one figure as shown above. How do I add many histograms in the same figure (so I can then add in the pdf page)? I see many tutorials on how to plot a grid of histograms within a figure but I haven't found one with all the histograms in one plot added to a figure.

Thanks, Stam

Answer 1

You can run the loop to plot all histograms together (your first code snippet) after having run the loop to plot them separately (your second code snippet). Here is an example where the random arrays are saved in the datasets list during the first loop to be able to plot them together in the second loop. This solution works by using plt.gcf() which returns the current figure.

import numpy as np               # v 1.19.2
import matplotlib.pyplot as plt  # v 3.3.4
from matplotlib.backends.backend_pdf import PdfPages

np.random.seed(1)

datasets = []
with PdfPages("exported_data.pdf") as pdf:
    # Plot each histogram, adding each figure to the pdf
    for i in range(6):
        datasets.append(np.random.normal(size=1000))
        plt.hist(datasets[i], bins=30, alpha = 0.5)
        pdf.savefig(plt.gcf())
        plt.close()
    # Plot histograms together using a loop then add the completed figure to the pdf
    for data in datasets:
        plt.hist(data, bins=30, alpha = 0.5)
    pdf.savefig(plt.gcf())
    plt.close()