How to add a data to the plot in matplotlib?-CodePudding

How can I have the line plot, with the data coming one by one? I have the code

import matplotlib.pyplot as plt

plt.ion()
plt.plot(1, 2)
plt.pause(2.5)
plt.plot(2, 5)
plt.pause(2.5)

but it does not show the line, if I add 'o' option in plot function or change the plot function to scatter function, it works fine, But I want a line with no markers, how can I do this?

CodePudding user response：

I tried the following code, according with my tests it works only if the plot is generated in an external window:

import matplotlib.pyplot as plt

plt.ion()
fig = plt.figure()
ax = fig.add_subplot(111)
ax.grid(True)

x = [4, 1, 5, 3, 8]
y = [1, 2, 9, 0, 2]

ax.set_xlim(0, 9)
ax.set_ylim(-1, 10)

for j in range(1, len(x)):
     X = [x[j-1], x[j]]
     Y = [y[j-1], y[j]]
     ax = plt.plot(X, Y, mew = 5, ms = 5)
     # mew and ms used to change crosses size
     plt.pause(1)# one second of delay
     plt.show()

If you are working on Spyder, in order to make the intepreter generating an external window whenever you call a plot you have to type

%matplotlib qt

on the intepreter (and not into the script file!) BEFORE running the previous lines of code

CodePudding user response：

To respond to the comment about "deleting the current plot", and to improve upon Stefano's answer a bit, we can use Matplotlib's object-oriented interface to do this:

import matplotlib.pyplot as plt

x = [0, 1, 2, 3, 4, 5, 6]
y = [3, 1, 4, 1, 5, 9, 2]

fig, ax = plt.subplots()
ax.set(xlim=(min(x), max(x)), ylim=(min(y), max(y)))

plt.ion()

(line,) = ax.plot([], [])  # initially an empty line

timestep = 0.5  # in seconds

for i in range(1, len(x)   1):
    line.set_data(x[:i], y[:i])
    plt.pause(timestep)
plt.show(block=True)

This version uses a single Line2D object and modifies its underlying data via set_data. Since Matplotlib doesn't have to draw multiple objects, just the one line, it should scale better once your data becomes large.