Matplotlib can only plot scatter graph

Question

[Python 2.7.12]

[Matplotlib 1.5.1]

Every scan cycle my code produces a 'top' score. I want to plot the performance over time. I have simplified the code into the example below:

import matplotlib.pyplot as plt
from matplotlib import lines
import random
count = 1

plt.axis([0, 1000, 0, 100])
plt.ion()

while True:
    count += 1
    a=random.randint(1, 50)
    plt.plot(count, a,'xb-')
    plt.pause(0.05)

plt.show()

My aim is to produce a line graph. The problem is whatever I set the line style to, it doesn't take effect. It only plots scatter type graphs. I am however able to change whether its a dot or an 'X' marker.

Or is the problem with the fact that the scores are 'plot and forget' so it has nothing to draw from?

EDIT: Plotting will be done in real-time

are you trying to do animation, or you just need a line graph? — Gerges
– Gerges, Commented Sep 29, 2017 at 17:26
I am not sure about the solution, but the problem is that a and count are scalars, so when plot is called, it is plotting a single point, and calling plot multiple times won't connect the dots, because it will generate a different line instance, — Gerges
– Gerges, Commented Sep 29, 2017 at 17:34

amin · Accepted Answer · 2017-09-29 18:47:01Z

2

You need at least 2 points to draw a line. You can store and use the previous state in each step.

import matplotlib.pyplot as plt
from matplotlib import lines
import random

x = 1

plt.axis([0, 1000, 0, 100])
plt.ion()

y_t1 = random.randint(1, 50)
plt.plot(1, y_t1, 'xb')
plt.pause(0.05)

while True:
    x += 1
    y_t2 = random.randint(1, 50)
    plt.plot([x - 1, x], [y_t1, y_t2], 'xb-')
    y_t1 = y_t2
    plt.pause(0.05)

plt.show()

edited Sep 29, 2017 at 18:47

answered Sep 29, 2017 at 18:37

amin

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