.. _pylab_examples-cursor_demo:

pylab_examples example code: cursor_demo.py
===========================================

[`source code <cursor_demo.py>`_]

::

    # -*- noplot -*-
    
    """
    This example shows how to use matplotlib to provide a data cursor.  It
    uses matplotlib to draw the cursor and may be a slow since this
    requires redrawing the figure with every mouse move.
    
    Faster cursoring is possible using native GUI drawing, as in
    wxcursor_demo.py.
    
    The mpldatacursor and mplcursors third-party packages can be used to achieve a
    similar effect.  See
        https://github.com/joferkington/mpldatacursor
        https://github.com/anntzer/mplcursors
    """
    from __future__ import print_function
    import matplotlib.pyplot as plt
    import numpy as np
    
    
    class Cursor(object):
        def __init__(self, ax):
            self.ax = ax
            self.lx = ax.axhline(color='k')  # the horiz line
            self.ly = ax.axvline(color='k')  # the vert line
    
            # text location in axes coords
            self.txt = ax.text(0.7, 0.9, '', transform=ax.transAxes)
    
        def mouse_move(self, event):
            if not event.inaxes:
                return
    
            x, y = event.xdata, event.ydata
            # update the line positions
            self.lx.set_ydata(y)
            self.ly.set_xdata(x)
    
            self.txt.set_text('x=%1.2f, y=%1.2f' % (x, y))
            plt.draw()
    
    
    class SnaptoCursor(object):
        """
        Like Cursor but the crosshair snaps to the nearest x,y point
        For simplicity, I'm assuming x is sorted
        """
    
        def __init__(self, ax, x, y):
            self.ax = ax
            self.lx = ax.axhline(color='k')  # the horiz line
            self.ly = ax.axvline(color='k')  # the vert line
            self.x = x
            self.y = y
            # text location in axes coords
            self.txt = ax.text(0.7, 0.9, '', transform=ax.transAxes)
    
        def mouse_move(self, event):
    
            if not event.inaxes:
                return
    
            x, y = event.xdata, event.ydata
    
            indx = np.searchsorted(self.x, [x])[0]
            x = self.x[indx]
            y = self.y[indx]
            # update the line positions
            self.lx.set_ydata(y)
            self.ly.set_xdata(x)
    
            self.txt.set_text('x=%1.2f, y=%1.2f' % (x, y))
            print('x=%1.2f, y=%1.2f' % (x, y))
            plt.draw()
    
    t = np.arange(0.0, 1.0, 0.01)
    s = np.sin(2*2*np.pi*t)
    fig, ax = plt.subplots()
    
    #cursor = Cursor(ax)
    cursor = SnaptoCursor(ax, t, s)
    plt.connect('motion_notify_event', cursor.mouse_move)
    
    ax.plot(t, s, 'o')
    plt.axis([0, 1, -1, 1])
    plt.show()
    

Keywords: python, matplotlib, pylab, example, codex (see :ref:`how-to-search-examples`)