Python matplotlib: Save to pdf in multiple pages

Question

I am trying to do the following:

I have created a figure, using matplotlib, with several subplots. More specifically, 2x4 subplots

The output is great for showing it on the screen, but not for saving it to pdf.

If I just use save_fig , it prints a single page pdf document, with the 2x4 grid.

What I would like to do, is re-arrange my subplots, to let's say a 2x4 grid (choosing which subplot goes where, would be good, but not necessary) and printing it to a 2-page pdf with 4 subplots each. (in order to be able to fit it to A4 page size)

Is this possible?

Thank you in advanced!

Answer 1

I would suggest to create 3 figures. One for showing and 2 for saving and plot the same data to them.

import matplotlib.pyplot as plt
import numpy as np


data = np.sort(np.cumsum(np.random.rand(24,16), axis=0), axis=0)

def plot(ax, x, y, **kwargs):
    ax.plot(x,y, **kwargs)

colors = ["crimson", "indigo", "limegreen", "gold"]
markers = ["o", "", "s", ""]
lines = ["", "-", "", ":"]

# figure 0 for showing
fig0, axes = plt.subplots(nrows=2,ncols=4)

for i, ax in enumerate(axes.flatten()):
    plot(ax, data[:,2*i], data[:,2*i+1], marker=markers[i%4], ls=lines[i%4],color=colors[i%4])


# figure 1 for saving
fig1, axes = plt.subplots(nrows=1,ncols=4)
for i, ax in enumerate(axes.flatten()):
    plot(ax, data[:,2*i], data[:,2*i+1], marker=markers[i], ls=lines[i],color=colors[i])

#figure 2 for saving
fig2, axes = plt.subplots(nrows=1,ncols=4)
for i, ax in enumerate(axes.flatten()):
    plot(ax, data[:,2*i+4], data[:,2*i+1+4], marker=markers[i], ls=lines[i],color=colors[i])

#save figures 1 and 2
fig1.savefig(__file__+"1.pdf")
fig2.savefig(__file__+"2.pdf")

#close figures 1 and 2
plt.close(fig1)
plt.close(fig2)
#only show figure 0
plt.show()

Answer 2

As I needed something similar for my work, I put some effort into automating the process of grouping plots into figures depending on the display medium. At first I had the idea to do each plot only once and just add the subplots to the figures to be saved in the pdf, but sadly, according to a comment in this answer , this is not possible, so everything needs to be re-plotted. The code shows the general idea of how this can be automated using PdfPages :

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


def niter(iterable, n):
    """
    Function that returns an n-element iterator, i.e.
    sub-lists of a list that are max. n elements long.
    """
    pos = 0
    while pos < len(iterable):
        yield iterable[pos:pos+n]
        pos += n


def plot_funcs(x, functions, funcnames, max_col, max_row):
    """
    Function that plots all given functions over the given x-range,
    max_col*max_row at a time, creating all needed figures while doing
    so.
    """

    ##amount of functions  to put in one plot    
    N = max_col*max_row

    ##created figures go here
    figs = []

    ##plotted-on axes go here
    used_axes = []

    ##looping through functions N at a time:
    for funcs, names in zip(niter(functions, N), niter(funcnames,N)):

        ##figure and subplots
        fig, axes = plt.subplots(max_col, max_row)

        ##plotting functions
        for name,func,ax in zip(names, funcs, axes.reshape(-1)):
            ax.plot(x, func(x))
            ax.set_title(name)
            used_axes.append(ax)

        ##removing empty axes:
        for ax in axes.reshape(-1):
            if ax not in used_axes:
                ax.remove()

        fig.tight_layout()
        figs.append(fig)

    return figs

##some functions to display
functions = [
    lambda x: x, lambda x: 1-x, lambda x: x*x, lambda x: 1/x, #4
    np.exp, np.sqrt, np.log, np.sin, np.cos,                  #5
    ]
funcnames = ['x','1-x', 'x$^2$', '1/x', 'exp', 'sqrt', 'log', 'sin','cos']

##layout for display on the screen
disp_max_col = 3
disp_max_row = 2

##layout for pdf
pdf_max_col = 2
pdf_max_row = 4

##displaying on the screen:
x = np.linspace(0,1,100)
figs = plot_funcs(x, functions, funcnames, disp_max_row, disp_max_col)
plt.show()


##saving to pdf if user wants to:
answer = input('Do you want to save the figures to pdf?')
if answer in ('y', 'Y', 'yes', ''):

    ##change number of subplots
    N = disp_max_col*disp_max_row
    figs = plot_funcs(x, functions, funcnames, pdf_max_row, pdf_max_col)

    ##from https://matplotlib.org/examples/pylab_examples/multipage_pdf.html
    with PdfPages('multipage_pdf.pdf') as pdf:
        for fig in figs:
            plt.figure(fig.number)
            pdf.savefig()

The core function, plot_funcs takes max_col and max_row keywords and then creates figures with the according amount of subplots. It then loops through a given list of functions to be plotted, each on its own subplot. Unused subplots are removed. Finally a list of all figures is returned.

In my example, I have 9 different functions, which I first show on the screen in a 2x3 layout (making a total of two figures, one with 6 subplots and one with 3 subplots). If the user is happy, the plots are redone in a 2x4 layout (again two figures, but this time one with 8 subplots and 1 with 1 subplot) and then saved to a file called multipage_pdf.pdf , following the example in the documentation .

Tested on python 3.5