How to plot 4 plots per row in matplotlib?

Question

I have 864 plots to plot. On running a loop, I can do plt.show() in the for loop, and print 864 plots, but that's difficult to view. Is there a way I can print 4 plots per row? (That would be 216 x 4). And how can I save them at the same time?

Edit: Example:

import matplotlib.pyplot as plt
i = 0

for i in range(100):
  plt.scatter(x[i],x[i])
  plt.scatter(y[i],y[i])
  plt.title('Vector: {}/100'.format(i+1))
  plt.show()

where x & y are list of list of cosine vectors.

@itamarkanter- tried that. For plots greater than 20, it significantly slows down? — Radhika, Jun 14 '21 at 09:14

score 0 · Answer 1 · answered Jun 14 '21 at 09:25

Commented inline

# 10 plots
for j in range(10):
  # close existing plots if any
  plt.close('all')
  plt.figure(figsize=(10,5))
  for i in range(4):
      # Plot with 1 row and 4 columns and current plot being drawn is (i+1)
      plt.subplot(1,4,i+1)
      x = np.random.randint(0,100, 100)
      y = np.random.randint(0,100, 100)
      plt.scatter(x,y)
      plt.scatter(y,x)
  # Finally save the plot
  plt.savefig(f"plot_{j}.png")

Adjust figsize based on length of your x and y axis.

edoelas · Accepted Answer · 2021-06-14T10:12:11.380

The easiest option that comes to my mind is using subplot:

import matplotlib.pyplot as plt

fig = plt.figure(figsize=(4,216))
axs = fig.axes
gs = fig.add_gridspec(ncols=4, nrows=216)
axs = gs.subplots()

There we are creating a figure with 4x216 plots. Probably you will need to adjust the figsize to your desired dimentions.

To plot something you just need to acces the axis using its index. For example:

x = [1, 2, 3]
y = [[1, 2], [3, 4], [5, 6]]

axs[0,0].plot(x, y)

To save it you can use fig.savefig("plot.png"). That creates a huge image. My suggestion is to create a pdf and store 4x6 plots per page. Here is an example of how to do it:

import matplotlib.pyplot as plt
from matplotlib.backends.backend_pdf import PdfPages
pp = PdfPages('plot.pdf')


for i in range(36):
    fig = plt.figure(figsize=(16,24))
    axs = fig.axes
    gs = fig.add_gridspec(ncols=4, nrows=6)
    axs = gs.subplots()

    pp.savefig()

pp.close()

This process takes some time since it has to render a lot of images. Plotting a line made of 1000 random points (previously calculated) in each figure takes 37s. Here is the code of the test:

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

start = time.time()

pp = PdfPages('plot.pdf')

xx = np.random.randint(0,100, 1000)
yy = np.random.randint(0,100, 1000)

for i in range(36):
    print(i)

    fig = plt.figure(figsize=(16,24))
    axs = fig.axes
    gs = fig.add_gridspec(ncols=4, nrows=6)
    axs = gs.subplots()

    for x in range(4):
        for y in range(6):
            axs[y,x].plot(xx, yy)
    
    pp.savefig()

pp.close()

print(time.time() - start)

How to plot 4 plots per row in matplotlib?

2 Answers2