.. _event_handling-lasso_demo:

event_handling example code: lasso_demo.py
==========================================

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

::

    """
    Show how to use a lasso to select a set of points and get the indices
    of the selected points.  A callback is used to change the color of the
    selected points
    
    This is currently a proof-of-concept implementation (though it is
    usable as is).  There will be some refinement of the API and the
    inside polygon detection routine.
    """
    from matplotlib.widgets import Lasso
    from matplotlib.nxutils import points_inside_poly
    from matplotlib.colors import colorConverter
    from matplotlib.collections import RegularPolyCollection
    
    from matplotlib.pyplot import figure, show
    from numpy import nonzero
    from numpy.random import rand
    
    class Datum:
        colorin = colorConverter.to_rgba('red')
        colorout = colorConverter.to_rgba('green')
        def __init__(self, x, y, include=False):
            self.x = x
            self.y = y
            if include: self.color = self.colorin
            else: self.color = self.colorout
    
    
    class LassoManager:
        def __init__(self, ax, data):
            self.axes = ax
            self.canvas = ax.figure.canvas
            self.data = data
    
            self.Nxy = len(data)
    
            facecolors = [d.color for d in data]
            self.xys = [(d.x, d.y) for d in data]
            fig = ax.figure
            self.collection = RegularPolyCollection(
                fig.dpi, 6, sizes=(100,),
                facecolors=facecolors,
                offsets = self.xys,
                transOffset = ax.transData)
    
            ax.add_collection(self.collection)
    
            self.cid = self.canvas.mpl_connect('button_press_event', self.onpress)
            self.ind = None
    
        def callback(self, verts):
            facecolors = self.collection.get_facecolors()
            ind = nonzero(points_inside_poly(self.xys, verts))[0]
            for i in range(self.Nxy):
                if i in ind:
                    facecolors[i] = Datum.colorin
                else:
                    facecolors[i] = Datum.colorout
    
            self.canvas.draw_idle()
            self.canvas.widgetlock.release(self.lasso)
            del self.lasso
            self.ind = ind
        def onpress(self, event):
            if self.canvas.widgetlock.locked(): return
            if event.inaxes is None: return
            self.lasso = Lasso(event.inaxes, (event.xdata, event.ydata), self.callback)
            # acquire a lock on the widget drawing
            self.canvas.widgetlock(self.lasso)
    
    if __name__ == '__main__':
    
        data = [Datum(*xy) for xy in rand(100, 2)]
    
        fig = figure()
        ax = fig.add_subplot(111, xlim=(0,1), ylim=(0,1), autoscale_on=False)
        lman = LassoManager(ax, data)
    
        show()
    

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