matplotlib heatmap, customize y axis - matplotlib

Question

Right now my code looks like this:
#generate 262*20 elements
values = np.random.random(262*20).tolist()
# convert the list to a 2D NumPy array
values = np.array(values).reshape((262, 20))
h, w = values.shape
#h=262, w=20
fig = plt.figure(num=None, dpi=80,figsize=(9, 7), facecolor='w', edgecolor='k')
ax = fig.add_subplot(111)
#fig, ax = plt.subplots()
plt.imshow(values)
plt.colorbar()
plt.xticks(np.arange(w), list('PNIYLKCVFWABCDEFGHIJ'))
ax.set_aspect(w/h)
plt.show()
The plot looks like this:
As you can see, the range of y axis is 0-261.
But I want my y axis to go from 26 to 290, missing 57, 239, and 253. So still 262 in total. I tried to generate a list like this:
mylist =[26, 27, ......missing 57, 239, 253, ....290]
plt.yticks(np.arange(h), mylist)
The Y axis just looks like everything squished together.
So I tried:
pylab.ylim([26, 290])
And It looks like this:
So it just feels like the data in first row always corresponds to [0], not to [26]

Answer 1

Suggest you use pcolormesh. If you want gaps, then use an numpy.ma.masked array for the area with gaps.
import matplotlib.pyplot as plt
import matplotlib.ticker as ticker
import numpy as np
values = np.random.rand(290,20)
values[:26, :] = np.NaN
values[ [57, 239, 253], :] = np.NaN
values = np.ma.masked_invalid(values)
h, w = values.shape
fig, ax = plt.subplots(figsize=(9,7))
# Make one larger so these values represent the edge of the data pixels.
y = np.arange(0, 290.5)
x = np.arange(0, 20.5)
pcm = ax.pcolormesh(x, y, values, rasterized=True) # you don't need rasterized=True
fig.colorbar(pcm)
plt.xticks(np.arange(w), list('PNIYLKCVFWABCDEFGHIJ'))
plt.show()
Result
EDIT: If you want to just work w/ a 262x20 array:
values = np.random.rand(262,20)
h, w = values.shape
fig, ax = plt.subplots(figsize=(9,7))
# Make one larger so these values represent the edge of the data pixels.
y = np.arange(0, 290.5)
y = np.delete(y, [57, 239, 253])
y = np.delete(y, range(26))
x = np.arange(0, 20.5)
pcm = ax.pcolormesh(x, y, values, rasterized=True) # you don't need rasterized=True
fig.colorbar(pcm)
plt.xticks(np.arange(w), list('PNIYLKCVFWABCDEFGHIJ'))
plt.show()
Note that this doesn't put a blank line at 57, 239 and 253. If you want that, you need to do:
values = np.random.rand(262,20)
Z = np.ones((290, 20)) * np.NaN
inds = set(range(290)) - set(list(range(26)) + [57, 239, 253])
for nn, ind in enumerate(inds):
Z[ind, :] = values[nn,:]
h, w = values.shape
fig, ax = plt.subplots(figsize=(9,7))
# Make one larger so these values represent the edge of the data pixels.
y = np.arange(0, 290.5)
x = np.arange(0, 20.5)
pcm = ax.pcolormesh(x, y, Z, rasterized=True) # you don't need rasterized=True
fig.colorbar(pcm)
plt.xticks(np.arange(w), list('PNIYLKCVFWABCDEFGHIJ'))
plt.show()