[FIXED] How to place lines below markers in Python?

Issue

I have to plot multiple lines and their curve fit lines on a single plot. All these lines are plotted using a for loop. Since it is plot using loops the curve fit lines of the succeeding step is plotted over its predecessor as shown in figure.

The reproducible code:

import matplotlib.pyplot as plt
import numpy as np

x = np.array([[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
             [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]])
y = np.array([[4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24],
             [6, 5.2, 8.5, 9.1, 13.4, 15.1, 16.1, 18.3, 20.4, 22.1, 23.7]])

m, n = x.shape

figure = plt.figure(figsize=(5.15, 5.15))
figure.clf()
plot = plt.subplot(111)
for i in range(m):
    poly = np.polyfit(x[i, :], y[i, :], deg =1)
    plt.plot(poly[0] * x[i, :] + poly[1], linestyle = '-')
    plt.plot(x[i, :], y[i, :], linestyle = '', marker = 'o', markersize = 20)
plot.set_ylabel('Y', labelpad = 6)
plot.set_xlabel('X', labelpad = 6)
plt.show()

I can fix this using another loop as:

import matplotlib.pyplot as plt
import numpy as np

x = np.array([[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
             [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]])
y = np.array([[4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24],
             [6, 5.2, 8.5, 9.1, 13.4, 15.1, 16.1, 18.3, 20.4, 22.1, 23.7]])

m, n = x.shape

figure = plt.figure(figsize=(5.15, 5.15))
figure.clf()
plot = plt.subplot(111)
for i in range(m):
    poly = np.polyfit(x[i, :], y[i, :], deg =1)
    plt.plot(poly[0] * x[i, :] + poly[1], linestyle = '-')
for i in range(m):
    plt.plot(x[i, :], y[i, :], linestyle = '', marker = 'o', markersize = 20)
plot.set_ylabel('Y', labelpad = 6)
plot.set_xlabel('X', labelpad = 6)
plt.show()

which gives me all the fit lines below the markers.

But is there any built-in function in Python/matplotlib to do this without using two loops?

Update

Only as an example I have used n = 2, n can be greater than 2, i.e. the loop would be run multiple times.

Update 2 after answer

Can I do this for the same line also? As an example:

 plt.plot(x[i, :], y[i, :], linestyle = ':', marker = 'o', markersize = 20)

Can I give the linestyle a zorder = 1 and the markers a zorder = 3?

Solution

Editing just your plotting lines:

    plt.plot(poly[0] * x[i, :] + poly[1], linestyle = '-',
             zorder=-1)
    plt.plot(x[i, :], y[i, :], linestyle = '', marker = 'o', markersize = 20,
             zorder=3)

now the markers are all in front of the lines, though within marker/line groups they're still order-of-plotting.

Update answer

No. One call to plot, one zorder argument.

If you want to match the color and style of markers and line in each pass through the loop, set up an iterator or generator for colors and get current_color on each pass, then use that as an argument for plot calls.

Answered By - cphlewis