Visualization of an array in matplotlib

Question

I am trying to visualize a random array with the square shape of (10, 10) in Python using matplotlib (3.5 version). I am also including the xaxis and yaxis ticks, but the ticks for 10 show empty data. Does anyone know how to sort it out?

Here's my code:

import numpy as np
from matplotlib import pyplot as plt
import matplotlib.pylab as pylab
params = {'legend.fontsize': 'medium',
 'figure.figsize': (15, 5),
 'axes.labelsize': 'x-large',
 'axes.titlesize':'x-large',
 'xtick.labelsize':'x-large',
 'ytick.labelsize':'x-large'}
pylab.rcParams.update(params)
arr = np.random.rand(10, 10)
plt.imshow(arr)
plt.ylim(0, 10)
plt.xlim(0, 10)
plt.xticks(np.arange(0.0, 11.0, 1.0))
plt.yticks(np.arange(0.0, 11.0, 1.0))
plt.show()

This is the produced image:

enter image description here

• TaxpayersMoney: Because arrays are zero indexed in python, and you are asking for an array of size 10, so 0-9?
• Ulises Bussi: The pyhton arrays starts it's indexin in 0. So you will have values between 0-9 in both axis, note that also every tick points to the center of "pixel". You could modify your lims plt.xlim((-0.5,9.5)) and plt.ylim((-0.5,9.5)). Last if you really need the numbers to be between 1 and 10 you could use xticks and yticks: plt.xticks(np.arange(10), np.arange(1,11)) and plt.yticks(np.arange(10), np.arange(1,11)) Note that if you want the tick to start at left-down corner of pixel you can play with the first arange in ticks (i think it must be np.arange(-0.5,9.5,1) but im not sure)

Answer 1

As other users pointed, Python arrays start indexing in '0'. You could trick the ticks to show the values you want:

1. create data to plot

   import numpy as np
   from matplotlib import pyplot as plt
   import matplotlib.pylab as pylab
   params = {'legend.fontsize': 'medium',
    'figure.figsize': (15, 5),
    'axes.labelsize': 'x-large',
    'axes.titlesize':'x-large',
    'xtick.labelsize':'x-large',
    'ytick.labelsize':'x-large'}
   pylab.rcParams.update(params)
   arr = np.random.rand(10, 10)
   

2. Then you can use plt.xticks(tickPosition,tickValues) and same with yticks. Note that every number point to the center of every value in your image so also you have to change your lim positions:

 plt.figure()
 plt.imshow(arr)
 plt.ylim(-0.5, 9.5) #to show no blank spaces
 plt.xlim(-0.5, 9.5) #to show no blank spaces
 
 plt.xticks(np.arange(0, 10),np.arange(1, 11)) #trick the ticks
 plt.yticks(np.arange(0, 10),np.arange(1, 11))

This will give you the next figure

Tricked points

3. Also you can set values at start (left-down corner) just tricking a little more:

 plt.xticks(np.arange(-0.5, 9.5),np.arange(1, 11))
 plt.yticks(np.arange(-0.5, 9.5),np.arange(1, 11))

this will give you this result:

with ticks at "start" of pixel