SciPy

scipy.stats.zscore

scipy.stats.zscore(a, axis=0, ddof=0)[source]

Calculates the z score of each value in the sample, relative to the sample mean and standard deviation.

Parameters :

a : array_like

An array like object containing the sample data.

axis : int or None, optional

If axis is equal to None, the array is first raveled. If axis is an integer, this is the axis over which to operate. Default is 0.

ddof : int, optional

Degrees of freedom correction in the calculation of the standard deviation. Default is 0.

Returns :

zscore : array_like

The z-scores, standardized by mean and standard deviation of input array a.

Notes

This function preserves ndarray subclasses, and works also with matrices and masked arrays (it uses asanyarray instead of asarray for parameters).

Examples

>>> a = np.array([ 0.7972,  0.0767,  0.4383,  0.7866,  0.8091,  0.1954,
                   0.6307, 0.6599,  0.1065,  0.0508])
>>> from scipy import stats
>>> stats.zscore(a)
array([ 1.1273, -1.247 , -0.0552,  1.0923,  1.1664, -0.8559,  0.5786,
        0.6748, -1.1488, -1.3324])

Computing along a specified axis, using n-1 degrees of freedom (ddof=1) to calculate the standard deviation:

>>> b = np.array([[ 0.3148,  0.0478,  0.6243,  0.4608],
                  [ 0.7149,  0.0775,  0.6072,  0.9656],
                  [ 0.6341,  0.1403,  0.9759,  0.4064],
                  [ 0.5918,  0.6948,  0.904 ,  0.3721],
                  [ 0.0921,  0.2481,  0.1188,  0.1366]])
>>> stats.zscore(b, axis=1, ddof=1)
array([[-0.19264823, -1.28415119,  1.07259584,  0.40420358],
       [ 0.33048416, -1.37380874,  0.04251374,  1.00081084],
       [ 0.26796377, -1.12598418,  1.23283094, -0.37481053],
       [-0.22095197,  0.24468594,  1.19042819, -1.21416216],
       [-0.82780366,  1.4457416 , -0.43867764, -0.1792603 ]])

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