Python's Matplotlib plotting in wrong order

Basically I have two arrays, one containing the values of the x-axis and the second containing the values of the y-axis. The problem is, when I do

plt.semilogy(out_samp,error_mc)

I get this

Which doesn't make any sense. That is because the plot functions plots everything as it encounters in the x array, not caring whether it's sorted in ascending order or not. How can I sort these two arrays so that the x array is sorted by increasing value and the y axis sorted in the same way so that the points are the same but the plot is connected so that it doesn't make this mess?

Thank you in advance!

Solution 1:

It is easier to zip, sort and unzip the two lists of data.

Example:

xs = [...]
ys = [...]

xs, ys = zip(*sorted(zip(xs, ys)))

plot(xs, ys)

See the zip documentation here: https://docs.python.org/3.5/library/functions.html#zip

Solution 2:

Sort by the value of x-axis before plotting. Here is an MWE.

import itertools

x = [3, 5, 6, 1, 2]
y = [6, 7, 8, 9, 10]

lists = sorted(itertools.izip(*[x, y]))
new_x, new_y = list(itertools.izip(*lists))

# import operator
# new_x = map(operator.itemgetter(0), lists)        # [1, 2, 3, 5, 6]
# new_y = map(operator.itemgetter(1), lists)        # [9, 10, 6, 7, 8]

# Plot
import matplotlib.pylab as plt
plt.plot(new_x, new_y)
plt.show()

For small data, zip (as mentioned by other answerers) is enough.

new_x, new_y = zip(*sorted(zip(x, y)))

The result,