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# scipy.cluster.vq.whiten

`scipy.cluster.vq.``whiten`(obs)

  Normalize a group of observations on a per feature basis.

  Before running k-means, it is beneficial to rescale each feature dimension of the observation set with whitening. Each feature is divided by its standard deviation across all observations to give it unit variance.

  > Parameters : | obs : ndarray Each row of the array is an observation. The columns are the features seen during each observation.
  >     >>> #         f0    f1    f2
  >     >>> obs = [[  1.,   1.,   1.],  #o0
  >     ...        [  2.,   2.,   2.],  #o1
  >     ...        [  3.,   3.,   3.],  #o2
  >     ...        [  4.,   4.,   4.]]) #o3
  Returns : | result : ndarray Contains the values in obs scaled by the standard deviation of each column.

  Examples

      >>> from scipy.cluster.vq import whiten
      >>> features  = np.array([[1.9, 2.3, 1.7],
      ...                       [1.5, 2.5, 2.2],
      ...                       [0.8, 0.6, 1.7,]])
      >>> whiten(features)
      array([[ 4.17944278,  2.69811351,  7.21248917],
             [ 3.29956009,  2.93273208,  9.33380951],
             [ 1.75976538,  0.7038557 ,  7.21248917]])

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