nums.numpy.std

nums.numpy.std(a, axis=None, dtype=None, out=None, ddof=0, keepdims=False)[source]

Compute the standard deviation along the specified axis.

This docstring was copied from numpy.std.

Some inconsistencies with the NumS version may exist.

Returns the standard deviation, a measure of the spread of a distribution, of the array elements. The standard deviation is computed for the flattened array by default, otherwise over the specified axis.

Parameters

  • a (BlockArray) – Calculate the standard deviation of these values.

  • axis (None or int or tuple of ints, optional) – Axis or axes along which the standard deviation is computed. The default is to compute the standard deviation of the flattened array. If this is a tuple of ints, a standard deviation is performed over multiple axes, instead of a single axis or all the axes as before.

  • dtype (dtype, optional) – Type to use in computing the standard deviation. For arrays of integer type the default is None.

  • out (BlockArray, optional) – Alternative output array in which to place the result. It must have the same shape as the expected output but the type (of the calculated values) will be cast if necessary.

  • ddof (int, optional) – Means Delta Degrees of Freedom. The divisor used in calculations is N - ddof, where N represents the number of elements. By default ddof is zero.

  • keepdims (bool, optional) – If this is set to True, the axes which are reduced are left in the result as dimensions with size one. With this option, the result will broadcast correctly against the input array. If the default value is passed, then keepdims will not be passed through to the std method of sub-classes of BlockArray, however any non-default value will be. If the sub-class’ method does not implement keepdims any exceptions will be raised.

Returns

standard_deviation – If out is None, return a new array containing the standard deviation, otherwise return a reference to the output array.

Return type

BlockArray, see dtype parameter above.

See also

var, mean, nanmean, nanstd, nanvar

Notes

The standard deviation is the square root of the average of the squared deviations from the mean, i.e., std = sqrt(mean(abs(x - x.mean())**2)).

The average squared deviation is normally calculated as x.sum() / N, where N = len(x). If, however, ddof is specified, the divisor N - ddof is used instead. In standard statistical practice, ddof=1 provides an unbiased estimator of the variance of the infinite population. ddof=0 provides a maximum likelihood estimate of the variance for normally distributed variables. The standard deviation computed in this function is the square root of the estimated variance, so even with ddof=1, it will not be an unbiased estimate of the standard deviation per se.

Note that, for complex numbers, std takes the absolute value before squaring, so that the result is always real and nonnegative.

‘out’ is currently not supported.

Examples

The doctests shown below are copied from NumPy. They won’t show the correct result until you operate get().

>>> a = nps.array([[1, 2], [3, 4]])  
>>> nps.std(a).get()  
array(1.1180339887498949) # may vary
>>> nps.std(a, axis=0).get()  
array([1.,  1.])
>>> nps.std(a, axis=1).get()  
array([0.5,  0.5])