Pagebreak inside Subplot? Matplotlib subplot over mulitple pages

Question

I want to create a python programm that is able to plot multiple graphs into one PDF file, however the number of subplots is variable. I did this already with one plot per page.

Answer 1

A. Loop over pages

You could find out how many pages you need (npages) and create a new figure per page.

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


tags = ["".join(np.random.choice(list("ABCDEFG123"), size=5)) for _ in range(53)]

N = len(tags)  # number of subplots
nrows = 5      # number of rows per page
ncols = 4      # number of columns per page

# calculate number of pages needed
npages = N // (nrows*ncols)
if N % (nrows*ncols) > 0:
    npages += 1

pdf = PdfPages('out2.pdf')

for page in range(npages):
    fig = plt.figure(figsize=(8,11))
    for i in range(min(nrows*ncols, N-page*(nrows*ncols))):
        # Your plot here
        count = page*ncols*nrows+i
        ax = fig.add_subplot(nrows, ncols, i+1)
        ax.set_title(f"{count} - {tags[count]}")
        ax.plot(np.cumsum(np.random.randn(33)))
        # end of plotting

    fig.tight_layout()
    pdf.savefig(fig)

pdf.close()
plt.show()

B. Loop over data

Or alternatively you could loop over the tags themselves and create a new figure once it's needed:

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


tags = ["".join(np.random.choice(list("ABCDEFG123"), size=5)) for _ in range(53)]

nrows = 5      # number of rows per page
ncols = 4      # number of columns per page

pdf = PdfPages('out2.pdf')

for i, tag in enumerate(tags):
    j = i % (nrows*ncols)
    if j == 0:
        fig = plt.figure(figsize=(8,11))

    ax = fig.add_subplot(nrows, ncols,j+1)
    ax.set_title(f"{i} - {tags[i]}")
    ax.plot(np.cumsum(np.random.randn(33)))
    # end of plotting
    if j == (nrows*ncols)-1 or i == len(tags)-1:
       fig.tight_layout()
       pdf.savefig(fig)

pdf.close()
plt.show()

Answer 2

You can use matplotlib's PdfPages as follows.

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

pp = PdfPages('multipage.pdf')

x=np.arange(1,10)
y=np.arange(1,10)

fig=plt.figure()
ax1=fig.add_subplot(211)
# ax1.set_title("cell" + keyInTags)
# ax1.plot(x, y, color='k')
# ax.plot(x, y_red, color='k')
ax2=fig.add_subplot(212)

pp.savefig(fig)

fig2=plt.figure()
ax1=fig2.add_subplot(321)
ax1.plot(x, y, color='k')
ax2=fig2.add_subplot(322)
ax2.plot(x, y, color='k')
ax3=fig2.add_subplot(313)

pp.savefig(fig2)

pp.close()

Play with these subplot numbers a little bit, so you would understand how to handle which graph goes where.