[FIXED] python matplotlib curve graph change line color on a specific value question

Issue

I want to know how to change plot(a,b) coordinates to plot(a,b,color='red') when the coordinates are above 40.0.

import matplotlib.pyplot as plt

a = [20.5,30.2,35.4,40.2,25.2,41.5,24.3,24.1,40.2]
b = list(range(len(a)))

plt.plot(b,a,marker='x',color='blue')
plt.show()

I don't know how to know the position value when the plot draws, and I'd like to try another way, but I don't know how to approach it.

Solution

To color the markers, you can create a color list that you pass to plt.scatter for the c parameter. I created the list using list comprehension. You didn't say how to handle the lines, so I just plotted them all as black in a separate plotting call.

import matplotlib.pyplot as plt

plt.close("all")

a = [20.5,30.2,35.4,40.2,25.2,41.5,24.3,24.1,40.2]
b = list(range(len(a)))
c = ["r" if value > 40 else "b" for value in a]

plt.plot(b, a, color="k")
plt.scatter(b, a, c=c, marker="x")
plt.show()

Answered By - jared