.. _event_handling-resample:

event_handling example code: resample.py
========================================

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

::

    import numpy as np
    import matplotlib.pyplot as plt
    from scikits.audiolab import wavread
    
    # A class that will downsample the data and recompute when zoomed.
    class DataDisplayDownsampler(object):
        def __init__(self, xdata, ydata):
            self.origYData = ydata
            self.origXData = xdata
            self.numpts = 3000
            self.delta = xdata[-1] - xdata[0]
    
        def resample(self, xstart, xend):
            # Very simple downsampling that takes the points within the range
            # and picks every Nth point
            mask = (self.origXData > xstart) & (self.origXData < xend)
            xdata = self.origXData[mask]
            ratio = int(xdata.size / self.numpts) + 1
            xdata = xdata[::ratio]
    
            ydata = self.origYData[mask]
            ydata = ydata[::ratio]
    
            return xdata, ydata
    
        def update(self, ax):
            # Update the line
            lims = ax.viewLim
            if np.abs(lims.width - self.delta) > 1e-8:
                self.delta = lims.width
                xstart, xend = lims.intervalx
                self.line.set_data(*self.downsample(xstart, xend))
                ax.figure.canvas.draw_idle()
    
    # Read data
    data = wavread('/usr/share/sounds/purple/receive.wav')[0]
    ydata = np.tile(data[:, 0], 100)
    xdata = np.arange(ydata.size)
    
    d = DataDisplayDownsampler(xdata, ydata)
    
    fig = plt.figure()
    ax = fig.add_subplot(1, 1, 1)
    
    #Hook up the line
    xdata, ydata = d.downsample(xdata[0], xdata[-1])
    d.line, = ax.plot(xdata, ydata)
    ax.set_autoscale_on(False) # Otherwise, infinite loop
    
    # Connect for changing the view limits
    ax.callbacks.connect('xlim_changed', d.update)
    
    plt.show()
    

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