title: How to clear up the data after I use PlotWidget.plot()?
body: <p>Here is my code:</p>
  
  <pre><code>import sys
  import numpy as np
  import pyqtgraph as pg
  from PyQt5.QtWidgets import QApplication, QWidget, QPushButton, QVBoxLayout
  
  
  class MyGraph(QWidget):
      def __init__(self):
          super(MyGraph, self).__init__()
          self.resize(600, 600)
  
          pg.setConfigOption('background', 'w')
  
          x = np.random.normal(size=1000)
          y = np.random.normal(size=1000)
  
          self.pw = pg.PlotWidget(self)
          self.pw.plot(x, y, pen=None, symbol='o', symbolBrush='r')
  
          self.plot_btn = QPushButton('Replot', self)
          self.plot_btn.clicked.connect(self.plot_slot)
  
          self.v_layout = QVBoxLayout()
          self.v_layout.addWidget(self.pw)
          self.v_layout.addWidget(self.plot_btn)
          self.setLayout(self.v_layout)
  
      def plot_slot(self):
          x = np.random.normal(size=1000)
          y = np.random.normal(size=1000)
  
          # The new data is added to the existed one
          self.pw.plot(x, y, pen=None, symbol='o', symbolBrush='r')
  
  
  if __name__ == '__main__':
      app = QApplication(sys.argv)
      demo = MyGraph()
      demo.show()
      sys.exit(app.exec_())
  </code></pre>
  
  <p>Every time I clicked the button, I want to clean the existed data and replot the new one, but PlotWidget doesn't seem to have the relative function to let me do that.</p>
  
  <p>Is there any way I can clean the data?</p>
  
  <p>Thanks!</p>