Plot the density of each feature independently as a volume.
 
  plotDensity(ds)
  patchHandles = plotDensity(ds);
 
  plotDensity(ds,'PARMNAME',PARAMVALUE)
    Additional parameters:
        nDensitySamples        - Number of linearly spaced
                                 samples used to construct the
                                 density estimate. Default 500.
        faceAlpha              - Face alpha value of the patch
                                 for each density. Must be a
                                 value between 0 and 1. Default
                                 0.5
        minimumKernelBandwidth - minimumBandwidth parameter of
                                 prtRvKde that is used to
                                 estimate each density. default
                                 []. See prtRvKde
 
  Example:
     ds = prtDataGenMary;
     plotDensity(ds)
 
     ds = prtDataGenIris;
     plotDensity(ds,'minimumKernelBandwidth',5e-3);