How to set xticks and yticks with my imshow plot?

Question

My code

import numpy as np
import matplotlib.pyplot as plt

with open('nm.dat','r') as f:
    vst = map(float, f)

print vst    

a=np.asarray(vst)
print len(a)

a11=a.reshape(4,22)

plt.imshow(a11, cmap='hot', interpolation='nearest')
plt.colorbar()
plt.show()

My image

I would like my x axis to be marked with equidistant 0,8,16,24,32,40,48,56,64,72,80,88 ticks.For y axis 0,2,4,6,8. How to solve this?

Answer 1

You are missing the extent argument in imshow. imshow assumes that there is a linear relation between pixels and your "physical" unit. You could just use:

plt.imshow(a11, cmap='hot', interpolation='nearest', extent=[0,88,0,8], origin='lower')

The extent variable has to be given such that extent=[xmin,xmax,ymin,ymax]. The origin='lower' argument is to specify that your [0,0] coordinate has to be placed in the bottom left of the axis. Otherwise, it is placed in the top left of the axis.

Finally, for showing only some particular ticks, you may want to use:

ax = plt.gca()
xticks = [0,8,16,24,32,40,48,56,64,72,80,88]
yticks = [0,2,4,6,8]
ax.xaxis.set_xticks(xticks)
ax.xaxis.set_yticks(yticks)