Why Is Numpy.ravel() Required In This Code That Produces Small Multiples?

I found some code to generate a set of small multiples and it is working perfectly. fig, axes = plt.subplots(6,3, figsize=(21,21)) fig.subplots_adjust(hspace=.3, wspace=.175) for a

Solution 1:

Your guess is correct. plt.subplots() returns either an Axes or a numpy array of several axes, depending on the input. In case a 2D grid is defined by the arguments nrows and ncols, the returned numpy array will be a 2D array as well.

This behaviour is explained in the pyplot.subplots documentation inside the squeeze argument,

squeeze : bool, optional, default: True
If True, extra dimensions are squeezed out from the returned Axes object:

• if only one subplot is constructed (nrows=ncols=1), the resulting single Axes object is returned as a scalar.

• for Nx1 or 1xN subplots, the returned object is a 1D numpy object array of Axes objects are returned as numpy 1D arrays.
• for NxM, subplots with N>1 and M>1 are returned as a 2D arrays.

If False, no squeezing at all is done: the returned Axes object is always a 2D array containing Axes instances, even if it ends up being 1x1.

Since here you have plt.subplots(6,3) and hence N>1, M>1, the resulting object is necessarily a 2D array, independent of what squeeze is set to.

This makes it necessary to flatten this array in order to be able to zip it. Options are

• zip(axes.ravel())
• zip(axes.flatten())
• zip(axes.flat)