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# numpy.nansum

numpy.nansum(a, axis=None, dtype=None, out=None, keepdims=<no value>, initial=<no value>, where=<no value>)

  Return the sum of array elements over a given axis treating Not a Numbers (NaNs) as zero.

  In NumPy versions <= 1.9.0 Nan is returned for slices that are all-NaN or empty. In later versions zero is returned.

  Parameters:
    a array_like

      Array containing numbers whose sum is desired. If a is not an array, a conversion is attempted.

    axis{int, tuple of int, None}, optional

      Axis or axes along which the sum is computed. The default is to compute the sum of the flattened array.

    dtype data-type, optional

      The type of the returned array and of the accumulator in which the elements are summed. By default, the dtype of a is used. An exception is when a has an integer type with less precision than the platform (u)intp. In that case, the default will be either (u)int32 or (u)int64 depending on whether the platform is 32 or 64 bits. For inexact inputs, dtype must be inexact.

    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 Output type determination for more details. The casting of NaN to integer can yield unexpected results.

    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 a.

      If the value is anything but the default, then keepdims will be passed through to the `mean` or `sum` methods of sub-classes of `ndarray`. If the sub-classes methods does not implement keepdims any exceptions will be raised.

    initial scalar, optional

      Starting value for the sum. See `reduce` for details.

      New in version 1.22.0.

    where array_like of bool, optional

      Elements to include in the sum. See `reduce` for details.

      New in version 1.22.0.

  Returns:
    nansum ndarray.

      A new array holding the result is returned unless out is specified, in which it is returned. The result has the same size as a, and the same shape as a if axis is not None or a is a 1-d array.

  See also

  `numpy.sum`

    Sum across array propagating NaNs.

  `isnan`

    Show which elements are NaN.

  `isfinite`

    Show which elements are not NaN or +/-inf.

  Notes

  If both positive and negative infinity are present, the sum will be Not A Number (NaN).

  Examples

      >>> import numpy as np
      >>> np.nansum(1)
      1
      >>> np.nansum([1])
      1
      >>> np.nansum([1, np.nan])
      1.0
      >>> a = np.array([[1, 1], [1, np.nan]])
      >>> np.nansum(a)
      3.0
      >>> np.nansum(a, axis=0)
      array([2.,  1.])
      >>> np.nansum([1, np.nan, np.inf])
      inf
      >>> np.nansum([1, np.nan, -np.inf])
      -inf
      >>> with np.errstate(invalid="ignore"):
      ...     np.nansum([1, np.nan, np.inf, -np.inf]) # both +/- infinity present
      np.float64(nan)