如何在Matplotlib图形中标记特定数据点

Question

I have a plot that I want to mark some values of x on the graph like in the following image, (ps I put the dots by hand) see the plot

I tried the following code, yet it did not work as I have expected.

roots = [-1,1,2]
plt.plot(vals,poly,markevery=roots,label='some graph')

I guess something wrong with the image I tried to post above; as a wrap up, I want to put a dot, on the function line which indicates that point is the root.

Answer 1

Assuming that the vals are integers in the range of [-60,60] , one would need to find the positions of [-1,1,2] in that list and use those positions as the argument to markevery .

import matplotlib.pyplot as plt

vals,poly = range(-60,60), range(-60,60)

plt.plot(vals, poly, label='some graph')
roots = [-1,1,2]

mark = [vals.index(i) for i in roots]
print(mark)
plt.plot(vals,poly,markevery=mark, ls="", marker="o", label="points")

plt.show()

Alternatively, you could also just plot only those values,

import matplotlib.pyplot as plt

vals,poly = range(-60,60), range(-60,60)

plt.plot(vals, poly, label='some graph')
roots = [-1,1,2]

mark = [vals.index(i) for i in roots]

plt.plot(roots,[poly[i] for i in mark], ls="", marker="o", label="points")

plt.show()