code: def _prepareData(self):
      x0, y0, x1, y1 = self._getNormalizedCoords()
      if x0.size == 0 or y0.size == 0:
          self._dataBounds = (None, None), (None, None)
          self._rectarray.resize(0)
          return
  
      xmn, xmx = np.min(x0), np.max(x1)
      ymn, ymx = np.min(y0), np.max(y1)
      self._dataBounds = (xmn, xmx), (ymn, ymx)
  
      self._rectarray.resize(max(x0.size, y0.size))
      memory = self._rectarray.ndarray()
      memory[:, 0] = x0
      memory[:, 1] = y0
      memory[:, 2] = x1 - x0
      memory[:, 3] = y1 - y0
  
imports: import numpy
  from ..None import functions
  from ..None import getConfigOption
  from ..None import Qt
  from ..Qt import QtCore, QtGui
  from .GraphicsObject import GraphicsObject
label_desc: Use image node_id 6 for calling the BarGraphItem obj's underlying member method code with example usage: obj._prepareData() without return types