matplotlib onclick event repeating

Question

I want to use the onclick method to select a range of data on my matplotlib graph. But the thing is, I can't do that more than once and update the plot. I have some ideas to do this, one of them would be to make a list of plots where I jump to new indices after I appended the new picture ... but mostly I would like to be able to store the information from the click (event.xdata) two times to color the area under the graph in that section - but for starters it would already be an achievement to draw points wherever I click. But I kind of think there is a better solution than putting a plt.draw() in the onclick function?

import numpy as np
import matplotlib.pyplot as plt
from itertools import islice

class ReadFile():
    def __init__(self, filename):
        self._filename = filename

    def read_switching(self):
        return np.genfromtxt(self._filename, unpack=True, usecols={0}, delimiter=',')

def onclick(event):
    global ix, iy
    ix, iy = event.xdata, event.ydata
    global coords
    coords.append((ix, iy))
    print(coords)
    fig.canvas.mpl_disconnect(cid)
    return coords

coords = []    
filename = 'test.csv'
fig = plt.figure()
ax = fig.add_subplot(111)
values = (ReadFile(filename).read_switching())
steps = np.arange(1, len(values)+1)*2
graph_1, = ax.plot(steps, values, label='original curve')
cid = fig.canvas.mpl_connect('button_press_event', onclick)
print(coords)
graph_2, = ax.plot(coords, marker='o')
plt.show()

For example I have the following function (picture) and I want to click on two coordinates and color the area under the graph, probably with a plt.draw().

Suever · Accepted Answer · 2016-03-13 20:24:07Z

1

The issue is that you're disconnecting the on_click event inside of your callback. Instead, you'll want to update the xdata and ydata of your graph_2 object. Then force the figure to be redrawn

import numpy as np
import matplotlib.pyplot as plt


fig = plt.figure()
ax = fig.add_subplot(111)

# Plot some random data
values = np.random.rand(4,1);
graph_1, = ax.plot(values, label='original curve')
graph_2, = ax.plot([], marker='o')

# Keep track of x/y coordinates
xcoords = []
ycoords = []

def onclick(event):
    xcoords.append(event.xdata)
    ycoords.append(event.ydata)

    # Update plotted coordinates
    graph_2.set_xdata(xcoords)
    graph_2.set_ydata(ycoords)

    # Refresh the plot
    fig.canvas.draw()

cid = fig.canvas.mpl_connect('button_press_event', onclick)
plt.show()

answered Mar 13, 2016 at 20:24

Suever

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3 Comments

xtlc Over a year ago

This was a great help, but I still don't understand how to get back the x and y coordinates from the function call? I want to store the clicks coordinates and use them in other functions. I know, I could use them in the same function.

Suever Over a year ago

@xtlc xcoords and ycoords are global variables so they should be accessible to all other functions already

xtlc Over a year ago

Sorry, I explained myself poorly: When I click, I can use the coordinates in the function, but everything that happens outside the function stops. For example what if I would want to print the coordinates outside from def onclick(event)? This is why I wanted something "like a loop".

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