diff options
Diffstat (limited to 'numpy/core/fromnumeric.py')
| -rw-r--r-- | numpy/core/fromnumeric.py | 114 |
1 files changed, 100 insertions, 14 deletions
diff --git a/numpy/core/fromnumeric.py b/numpy/core/fromnumeric.py index 573868b61..c96505521 100644 --- a/numpy/core/fromnumeric.py +++ b/numpy/core/fromnumeric.py @@ -691,12 +691,38 @@ def round_(a, decimals=0, out=None): around = round_ def mean(a, axis=None, dtype=None, out=None): - """mean(a, axis=None, dtype=None) - Return the arithmetic mean. + """Compute the mean along the specified axis. - The mean is the sum of the elements divided by the number of elements. + Returns the average of the array elements. The average is taken over the + flattened array by default, otherwise over the specified axis. + + :Parameters: + axis : integer + Axis along which the means are computed. The default is + to compute the standard deviation of the flattened array. + dtype : type + Type to use in computing the means. For arrays of + integer type the default is float32, for arrays of float types it + is the same as the array type. + out : ndarray + Alternative output array in which to place the result. It must have + the same shape as the expected output but the type will be cast if + necessary. + + :Returns: + mean : The return type varies, see above. + A new array holding the result is returned unless out is specified, + in which case a reference to out is returned. + + :SeeAlso: + - var : variance + - std : standard deviation + + Notes + ----- + The mean is the sum of the elements along the axis divided by the + number of elements. - See also: average """ try: mean = a.mean @@ -704,14 +730,44 @@ def mean(a, axis=None, dtype=None, out=None): return _wrapit(a, 'mean', axis, dtype, out) return mean(axis, dtype, out) + def std(a, axis=None, dtype=None, out=None): - """std(sample, axis=None, dtype=None) - Return the standard deviation, a measure of the spread of a distribution. + """Compute the standard deviation along the specified axis. + + Returns the standard deviation of the array elements, a measure of the + spread of a distribution. The standard deviation is computed for the + flattened array by default, otherwise over the specified axis. + + :Parameters: + axis : integer + Axis along which the standard deviation is computed. The default is + to compute the standard deviation of the flattened array. + dtype : type + Type to use in computing the standard deviation. For arrays of + integer type the default is float32, for arrays of float types it + is the same as the array type. + out : ndarray + Alternative output array in which to place the result. It must have + the same shape as the expected output but the type will be cast if + necessary. + + :Returns: + standard deviation : The return type varies, see above. + A new array holding the result is returned unless out is specified, + in which case a reference to out is returned. + + :SeeAlso: + - var : variance + - mean : average + + Notes + ----- - The standard deviation is the square root of the average of the squared - deviations from the mean, i.e. std = sqrt(mean((x - x.mean())**2)). + The standard deviation is the square root of the average of the squared + deviations from the mean, i.e. var = sqrt(mean((x - x.mean())**2)). The + computed standard deviation is biased, i.e., the mean is computed by + dividing by the number of elements, N, rather than by N-1. - See also: var """ try: std = a.std @@ -719,14 +775,44 @@ def std(a, axis=None, dtype=None, out=None): return _wrapit(a, 'std', axis, dtype, out) return std(axis, dtype, out) + def var(a, axis=None, dtype=None, out=None): - """var(sample, axis=None, dtype=None) - Return the variance, a measure of the spread of a distribution. + """Compute the variance along the specified axis. + + Returns the variance of the array elements, a measure of the spread of a + distribution. The variance is computed for the flattened array by default, + otherwise over the specified axis. + + :Parameters: + axis : integer + Axis along which the variance is computed. The default is to + compute the variance of the flattened array. + dtype : type + Type to use in computing the variance. For arrays of integer type + the default is float32, for arrays of float types it is the same as + the array type. + out : ndarray + Alternative output array in which to place the result. It must have + the same shape as the expected output but the type will be cast if + necessary. + + :Returns: + variance : depends, see above + A new array holding the result is returned unless out is specified, + in which case a reference to out is returned. + + :SeeAlso: + - std : standard deviation + - mean : average + + Notes + ----- - The variance is the average of the squared deviations from the mean, - i.e. var = mean((x - x.mean())**2). + The variance is the average of the squared deviations from the mean, i.e. + var = mean((x - x.mean())**2). The computed variance is biased, i.e., + the mean is computed by dividing by the number of elements, N, rather + than by N-1. - See also: std """ try: var = a.var |