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I am plotting data on a tkinter app, using matplotlib.

As long as I start the plot with a dataset, it is just fine, but when I try to change the dataset, instead of getting a new plot in place of the old one, a new plot get add on the application, so they end up stacked.

How do I update the matplotlib figure, with new dataset? I use a button to trigger the plot, passing the data to the function. This is the relevant part of the app:

class Application(Frame):

    def __init__(self, master=None):

        Frame.__init__(self, master)
        matplotlib.rcParams["figure.figsize"] = [2,6]
        self.data_set = [1,2,3,4,5,6]
        self.initUI()


    def initUI(self):
        self.pack(fill=BOTH, expand=1)
        self.style = Style()
        self.style.theme_use("default")

        plotbutton = Button(self, text="Plot Data", command=lambda: self.create_plot(self.data_set))
        calculatebutton.place(x=300, y=600)

        quitbutton = Button(self, text="Quit", command=self.quit)
        quitbutton.place(x=400, y=600)

    def create_plot(self, dataset):

        plt = Figure(figsize=(4, 4), dpi=100)
        a = plt.add_subplot(211)
        a.plot(dataset, '-o', label="Main response(ms)")
        a.set_ylabel("milliseconds")
        a.set_title("plot")
        canvas = FigureCanvasTkAgg(plt, self)
        canvas.show()
        canvas.get_tk_widget().pack(fill=BOTH)
        toolbar = NavigationToolbar2TkAgg(canvas, self)
        toolbar.update()
        canvas._tkcanvas.pack(fill=BOTH)
        # generate a random list of 6 numbers for sake of simplicity, for the next plot
        data_set = random.sample(range(30), 6)
        return


def main():

    root = Tk()
    root.wm_title("generic app")
    root.geometry("800x700+100+100")

    app = Application(master=root)
    app.mainloop()

    return 0
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  • matplotlib has function clear() which remove old plot Commented Jan 4, 2017 at 7:55
  • When should I use it? in my create_plot function, before the add_subplot call? Commented Jan 4, 2017 at 8:00
  • you didn' create working example so it is hard to say. But I made own version and now I see that you problem is different than I was thinking. Commented Jan 4, 2017 at 8:07
  • problem is that every time you click button, you create new Figure, plot and canvas - so clear() make no sence - and you use pack() to add it but you don't remove old one. pack() is used to add new element below other elements - it doesn't replace elements. You have to use pack_forget() to remove old canvas. (Or maybe better use destroy()) Commented Jan 4, 2017 at 8:11
  • I see; so the issue is in the way that I add the plot to the app. I did grab this approach from an example on the matplotlib site and a youtube tutorial. I can try with forget or destroy and see what happens; although I do not save the reference to the previous canvas, so I am not sure how do I retrieve the reference to destroy it Commented Jan 4, 2017 at 8:21

1 Answer 1

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2

You have to remove/destroy old plot before you create new one.

It works for me - maybe it is what you need

I use 

    self.widget = None
    self.toolbar = None

to keep access to widgets

I commented some lines of code because it works for me without them.

import matplotlib
matplotlib.use('TkAgg')
from matplotlib.backends.backend_tkagg import Figure, FigureCanvasTkAgg, NavigationToolbar2TkAgg
from tkinter import *
import random

class Application(Frame):

    def __init__(self, master=None):

        Frame.__init__(self, master)
        matplotlib.rcParams["figure.figsize"] = [2,6]
        self.data_set = [1,2,3,4,5,6]
        self.initUI()

        # to assign widgets
        self.widget = None
        self.toolbar = None

    def initUI(self):
        self.pack(fill=BOTH, expand=1)

        plotbutton = Button(self, text="Plot Data", command=lambda: self.create_plot(self.data_set))
        plotbutton.place(x=300, y=600)

        quitbutton = Button(self, text="Quit", command=self.quit)
        quitbutton.place(x=400, y=600)


    def create_plot(self, dataset):

        # remove old widgets
        if self.widget:
            self.widget.destroy()

        if self.toolbar:
            self.toolbar.destroy()

        # create new elements

        plt = Figure(figsize=(4, 4), dpi=100)

        a = plt.add_subplot(211)
        a.plot(dataset, '-o', label="Main response(ms)")
        a.set_ylabel("milliseconds")
        a.set_title("plot")

        canvas = FigureCanvasTkAgg(plt, self)

        self.toolbar = NavigationToolbar2TkAgg(canvas, self)
        #toolbar.update()

        self.widget = canvas.get_tk_widget()
        self.widget.pack(fill=BOTH)

        #self.toolbars = canvas._tkcanvas
        #self.toolbars.pack(fill=BOTH)

        # generate a random list of 6 numbers for sake of simplicity, for the next plot
        self.data_set = random.sample(range(30), 6)


def main():

    root = Tk()
    root.wm_title("generic app")
    root.geometry("800x700+100+100")

    app = Application(master=root)
    app.mainloop()

main()

Or maybe you should create Figure/canvas/etc. only once and replace data in plot using clear() and set_data()

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