[FIXED] Python subplot used to show one figure

Issue

When I was using the subplot, and tried to use the following subplot to plot only one figure, it will give error:

AttributeError: 'AxesSubplot' object has no attribute 'flat'

fig, ax = plt.subplots(nrows=nrows, ncols=ncols,figsize=figsize)
for i, ax in enumerate(ax.flat):
    ax.plot(X, Y, color='k')

How to solve this issue if I want to arbitrarily set the number of sub figures?How can I easily understand ax.flat?

Solution

flat is an attribute of numpy arrays which returns an iterator. For example, if you have a 2d array like this:

import numpy as np
arr2d = np.arange(4).reshape(2, 2)
arr2d
# array([[0, 1],
#        [2, 3]])

the flat attribute is provided as a convenient way to iterate through this array as if it was a 1d array:

for value in arr2d.flat:
    print(value)
# 0
# 1
# 2
# 3

You can also flatten the array with the flatten method:

arr2d.flatten()
# array([0, 1, 2, 3])

So going back to your question, when you specify:

• ncols to 1 and nrows to a value greater than 1 or the other way around, you get the axes in a 1d numpy array, in which case the flat attribute returns the same array.
• both ncols and nrows to values greater than 1, you get the axes in a 2d array, in which case the flat attribute returns the flattened array.
• both ncols and nrows to 1, you get the axes object, which doesn't have a flat attribute.

So a possible solution would be to turn your ax object into a numpy array everytime:

fig, ax = plt.subplots(nrows=nrows, ncols=ncols, figsize=figsize)

ax = np.array(ax)
for i, axi in enumerate(ax.flat):
    axi.plot(...)

Answered By - josemz