# Matplotlib: multiple subplots with one axis label¶

## Using a single axis label to annotate multiple subplot axes¶

When using multiple subplots with the same axis units, it is redundant to label each axis individually, and makes the graph overly complex. You can use a single axis label, centered in the plot frame, to label multiple subplot axes. Here is how to do it:

In [ ]:
#!python
# note that this a code fragment...you will have to define your own data to plot
# Set up a whole-figure axes, with invisible axis, ticks, and ticklabels,
# which we use to get the xlabel and ylabel in the right place
bigAxes = pylab.axes(frameon=False)     # hide frame
pylab.xticks([])                        # don't want to see any ticks on this axis
pylab.yticks([])
# I'm using TeX for typesetting the labels--not necessary
pylab.ylabel(r'\textbf{Surface Concentration $(nmol/m^2)$}', size='medium')
pylab.xlabel(r'\textbf{Time (hours)}', size='medium')
# Create subplots and shift them up and to the right to keep tick labels
# from overlapping the axis labels defined above
topSubplot = pylab.subplot(2,1,1)
position = topSubplot.get_position()
position[0] = 0.15
position[1] = position[1] + 0.01
topSubplot.set_position(position)
pylab.errorbar(times150, average150)
bottomSubplot = pylab.subplot(2,1,2)
position = bottomSubplot.get_position()
position[0] = 0.15
position[1] = position[1] + 0.03
bottomSubplot.set_position(position)
pylab.errorbar(times300, average300)


Alternatively, you can use the following snippet to have shared ylabels on your subplots. Also see the attached figure output. )#

In [ ]:
#!python
import pylab

figprops = dict(figsize=(8., 8. / 1.618), dpi=128)                                          # Figure properties
adjustprops = dict(left=0.1, bottom=0.1, right=0.97, top=0.93, wspace=0.2 hspace=0.2)       # Subplot properties

fig = pylab.figure(**figprops)                                                              # New figure

bx = fig.add_subplot(3, 1, 2, sharex=ax, sharey=ax)
cx = fig.add_subplot(3, 1, 3, sharex=ax, sharey=ax)

ax.plot([0,1,2], [2,3,4], 'k-')
bx.plot([0,1,2], [2,3,4], 'k-')
cx.plot([0,1,2], [2,3,4], 'k-')

pylab.setp(ax.get_xticklabels(), visible=False)
pylab.setp(bx.get_xticklabels(), visible=False)

bx.set_ylabel('This is a long label shared among more axes', fontsize=14)
cx.set_xlabel('And a shared x label', fontsize=14)


Thanks to Sebastian Krieger from matplotlib-users list for this trick.

Simple function to get rid of superfluous xticks but retain the ones on the bottom (works in pylab). Combine it with the above snippets to get a nice plot without too much redundance:

In [ ]:
#!python
def rem_x():
'''Removes superfluous x ticks when multiple subplots  share
their axis works only in pylab mode but can easily be rewritten
for api use'''
nr_ax=len(gcf().get_axes())
count=0
for z in gcf().get_axes():
if count == nr_ax-1: break
setp(z.get_xticklabels(),visible=False)
count+=1


The first one above doesn't work for me. The subplot command overwrites the bigaxes. However, I found a much simpler solution to do a decent job for two axes and one ylabel:

yyl=plt.ylabel(r'My longish label that I want vertically centred')

yyl.set_position((yyl.get_position()[0],1)) # This says use the top of the bottom axis as the reference point.

yyl.set_verticalalignment('center')

Section author: Unknown[78], DavidLinke, Unknown[80], Unknown[109], Unknown[110]

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