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Reverse Y-Axis in PyPlot

Posted by: admin November 1, 2017 Leave a comment

Questions:

I have a scatter plot graph with a bunch of random x, y coordinates. Currently the Y-Axis starts at 0 and goes up to the max value. I would like the Y-Axis to start at the max value and go up to 0.

points = [(10,5), (5,11), (24,13), (7,8)]    
x_arr = []
y_arr = []
for x,y in points:
    x_arr.append(x)
    y_arr.append(y)
plt.scatter(x_arr,y_arr)
Answers:

There is a new API that makes this even simpler.

plt.gca().invert_xaxis()

and/or

plt.gca().invert_yaxis()

Questions:
Answers:

DisplacedAussie‘s answer is correct, but usually a shorter method is just to reverse the single axis in question:

plt.scatter(x_arr, y_arr)
ax = plt.gca()
ax.set_ylim(ax.get_ylim()[::-1])

where the gca() function returns the current Axes instance and the [::-1] reverses the list.

Questions:
Answers:

Use matplotlib.pyplot.axis()

axis([xmin, xmax, ymin, ymax])

So you could add something like this at the end:

plt.axis([min(x_arr), max(x_arr), max(y_arr), 0])

Although you might want padding at each end so that the extreme points don’t sit on the border.

Questions:
Answers:

If you’re in ipython in pylab mode, then

plt.gca().invert_yaxis()
show()

the show() is required to make it update the current figure.

Questions:
Answers:

Another similar method to those described above is to use plt.ylim for example:

plt.ylim(max(y_array), min(y_array))

This method works for me when I’m attempting to compound multiple datasets on Y1 and/or Y2

Questions:
Answers:

Alternatively, you can use the matplotlib.pyplot.axis() function, which allows you inverting any of the plot axis

ax = matplotlib.pyplot.axis()
matplotlib.pyplot.axis((ax[0],ax[1],ax[3],ax[2]))

Or if you prefer to only reverse the X-axis, then

matplotlib.pyplot.axis((ax[1],ax[0],ax[2],ax[3]))

Indeed, you can invert both axis:

matplotlib.pyplot.axis((ax[1],ax[0],ax[3],ax[2]))

Questions:
Answers:

using ylim() might be the best approach for your purpose:

xValues = list(range(10))
quads = [x** 2 for x in xValues]
plt.ylim(max(quads), 0)
plt.plot(xValues, quads)

will result:enter image description here