#### Previous topic

numpy.average

#### Next topic

numpy.std

# numpy.mean

`numpy.``mean`(a, axis=None, dtype=None, out=None, keepdims=False)

  Compute the arithmetic mean along the specified axis.

  Returns the average of the array elements. The average is taken over the flattened array by default, otherwise over the specified axis. `float64` intermediate and return values are used for integer inputs.

  Parameters: | a : array_like Array containing numbers whose mean is desired. If a is not an array, a conversion is attempted. axis : int, optional Axis along which the means are computed. The default is to compute the mean of the flattened array. dtype : data-type, optional Type to use in computing the mean. For integer inputs, the default is `float64`; for floating point inputs, it is the same as the input dtype. out : ndarray, optional Alternate output array in which to place the result. The default is `None`; if provided, it must have the same shape as the expected output, but the type will be cast if necessary. See `doc.ufuncs` for details. 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 original arr.
  Returns: | m : ndarray, see dtype parameter above If out=None, returns a new array containing the mean values, otherwise a reference to the output array is returned.

  See also

  `average`
    Weighted average

  `std`, `var`, `nanmean`, `nanstd`, `nanvar`

  Notes

  The arithmetic mean is the sum of the elements along the axis divided by the number of elements.

  Note that for floating-point input, the mean is computed using the same precision the input has. Depending on the input data, this can cause the results to be inaccurate, especially for `float32` (see example below). Specifying a higher-precision accumulator using the `dtype` keyword can alleviate this issue.

  Examples

      >>> a = np.array([[1, 2], [3, 4]])
      >>> np.mean(a)
      2.5
      >>> np.mean(a, axis=0)
      array([ 2.,  3.])
      >>> np.mean(a, axis=1)
      array([ 1.5,  3.5])

  In single precision, `mean` can be inaccurate:

      >>> a = np.zeros((2, 512*512), dtype=np.float32)
      >>> a[0, :] = 1.0
      >>> a[1, :] = 0.1
      >>> np.mean(a)
      0.546875

  Computing the mean in float64 is more accurate:

      >>> np.mean(a, dtype=np.float64)
      0.55000000074505806