def plot(self, f, lfilter=None,**kargs):
        """Applies a function to each packet to get a value that will be plotted with matplotlib. A matplotlib object is returned
        lfilter: a truth function that decides whether a packet must be ploted"""

        return plt.plot([ f(i) for i in self.res if not lfilter or lfilter(i) ], **kargs)