Plotting an array with pcolormesh with x and y data removes a row of the data
To illustrate what I mean, see the following:
data = np.random.random([5,5])
results in this 5x5 grid:
But if I want to define the x an y axes for the data like this, pcolormesh creates a 4x4 grid, with the top and right rows missing...
plt.pcolormesh(range(5), range(5), data)
In order to get the full 5x5 plot, I have to do
plt.pcolormesh(range(6), range(6), data)
Is this just a quirk of pcolormesh? Or can someone explain the reasoning why pcolormesh behaves this way?
The behaviour you see is expected. The pcolor documentation states for
pcolor(X, Y, C, **kwargs):
Ideally the dimensions of X and Y should be one greater than those of C; if the dimensions are the same, then the last row and column of C will be ignored.
The same is of course true for
I'm not sure if this is the place to discuss whether this behaviour is a "quirk", but the underlying idea is that the grid defines the edges of the colored faces. Just as on a number line you have
n numbers and
n-1 intervals in between.
It actually makes sense to define the edges by the grid, because
pcolormesh also allows for unequally spaced grids which would be impossible to define otherwise.