How to extract data from matplotlib plot

问题:

I have a wxPython program which reads from different datasets, performs various types of simple on-the-fly analysis on the data and plots various combinations of the datasets to matplotlib canvas. I would like to have the opportunity to dump currently plotted data to file for more sophisticated analysis later on.

The question is: are there any methods in matplotlib that allow access to the data currently plotted in matplotlib.Figure?

回答1:

Jakub is right about modifying the Python script to write out the data directly from the source from which it was sent into the plot; that's the way I'd prefer to do this. But for reference, if you do need to get data out of a plot, I think this should do it

gca().get_lines()[n].get_xydata()

Alternatively you can get the x and y data sets separately:

line = gca().get_lines()[n]
xd = line.get_xdata()
yd = line.get_ydata()

回答2:

Its Python, so you can modify the source script directly so the data is dumped before it is plotted

回答3:

The matplotlib.pyplot.gca can be used to extract data from matplotlib plots. Here is a simple example:

import matplotlib.pyplot as plt
plt.plot([1,2,3],[4,5,6])
ax = plt.gca()
line = ax.lines[0]
line.get_xydata()

On running this, you will see 2 outputs - the plot and the data:

array([[1., 4.],
   [2., 5.],
   [3., 6.]])

You can also get the x data and y data seperately. On running line.get_xdata(), you will get:

array([1, 2, 3])

And on running line.get_ydata(), you will get:

array([4, 5, 6])

Note: gca stands for get current axis

回答4:

I know this is an old question, but I feel there is a solution better than the ones offered here so I decided to write this answer.

You can use unittest.mock.patch to temporarily replace the matplotlib.axes.Axes.plot function:

from unittest.mock import patch

def save_data(self, *args, **kwargs):
    # save the data that was passed into the plot function
    print(args)

with patch('matplotlib.axes.Axes.plot', new=save_data):
    # some code that will eventually plot data
    a_function_that_plots()

Once you exit the with block, Axes.plot will resume normal behavior.