I have constructed a set of pie charts with some help Insert image into pie chart slice
My charts look wonderful, now I need to place all 6 of them in a 2×3 figure with common tick marks on the shared x and y axis.
For starting I am looking at subplots and thought I could get it to work. I downloaded some examples and started to try a few things.
f, (a) = (plt.subplots(nrows=1, ncols=1, sharex=True, sharey=True))#,
#squeeze=False, subplot_kw=None, gridspec_kw=None))
print(type(f),'n',type(a),'n')#,type(b))
yields:
class ‘matplotlib.figure.Figure’
class ‘matplotlib.axes._subplots.AxesSubplot’
while:
f, (a) = (plt.subplots(nrows=1, ncols=1, sharex=True, sharey=True, squeeze=False, subplot_kw=None, gridspec_kw=None))
print(type(f),'n',type(a),'n')#,type(b))
returns:
class ‘matplotlib.figure.Figure’
class ‘numpy.ndarray’
When I do this:
f, (a,b) = (plt.subplots(nrows=2, ncols=1, sharex=True, sharey=True, squeeze=False, subplot_kw=None, gridspec_kw=None))
print(type(f),'n',type(a),'n',type(b))
I get the similar results, however if nrows=1 and ncols=2 I get an error:
f, (a,b) = (plt.subplots(nrows=1, ncols=2, sharex=True, sharey=True, squeeze=False, subplot_kw=None, gridspec_kw=None))
print(type(f),'n',type(a),'n',type(b))
ValueError: not enough values to unpack (expected 2, got 1)
but again this:
f, (a , b) = (
plt.subplots(nrows=1, ncols=2, sharex=True, sharey=True))#,
#squeeze=False, subplot_kw=None, gridspec_kw=None))
print(type(f),'n',type(a),'n',type(b))
gives
class ‘matplotlib.figure.Figure’
class ‘matplotlib.axes._subplots.AxesSubplot’
class ‘matplotlib.axes._subplots.AxesSubplot’
Why is it either or array or axes, and also why does a 2X1 work and a 1X2 does not?
I wish to high heaven I could better understand the documentation. Thanks.
Answers:
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Method 1
The different return types are due to the squeeze keyword argument to plt.subplots() which is set to True by default.
Let’s enhance the documentation with the respective unpackings:
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.
fig, ax = plt.subplots()- for Nx1 or 1xN subplots, the returned object is a 1D numpy object array of Axes objects are returned as numpy 1D arrays.
fig, (ax1, ..., axN) = plt.subplots(nrows=N, ncols=1)(for Nx1)
fig, (ax1, ..., axN) = plt.subplots(nrows=1, ncols=N)(for 1xN)- for NxM, subplots with N>1 and M>1 are returned as a 2D arrays.
fig, ((ax11, .., ax1M),..,(axN1, .., axNM)) = plt.subplots(nrows=N, ncols=M)- 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 1×1.
fig, ((ax,),) = plt.subplots(nrows=1, ncols=1, squeeze=False)
fig, ((ax,), .. ,(axN,)) = plt.subplots(nrows=N, ncols=1, squeeze=False)for Nx1
fig, ((ax, .. ,axN),) = plt.subplots(nrows=1, ncols=N, squeeze=False)for 1xN
fig, ((ax11, .., ax1M),..,(axN1, .., axNM)) = plt.subplots(nrows=N, ncols=M)
Alternatively you may always use the unpacked version
fig, ax_arr = plt.subplots(nrows=N, ncols=M, squeeze=False)
and index the array to obtain the axes, ax_arr[1,2].plot(..).
So for a 2 x 3 grid it wouldn’t actually matter if you set squeeze to False. The result will always be a 2D array. You may unpack it as
fig, ((ax1, ax2, ax3),(ax4, ax5, ax6)) = plt.subplots(nrows=2, ncols=3)
to have ax{i} as the matplotlib axes objects, or you may use the packed version
fig, ax_arr = plt.subplots(nrows=2, ncols=3) ax_arr[0,0].plot(..) # plot to first top left axes ax_arr[1,2].plot(..) # plot to last bottom right axes
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0