Source code for xorbits._mars.tensor.indexing.flatnonzero

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# Licensed under the Apache License, Version 2.0 (the "License");
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#      http://www.apache.org/licenses/LICENSE-2.0
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from .nonzero import nonzero


def flatnonzero(a):
    """
    Return indices that are non-zero in the flattened version of a.

    This is equivalent to a.ravel().nonzero()[0].

    Parameters
    ----------
    a : Tensor
        Input tensor.

    Returns
    -------
    res : Tensor
        Output tensor, containing the indices of the elements of `a.ravel()`
        that are non-zero.

    See Also
    --------
    nonzero : Return the indices of the non-zero elements of the input tensor.
    ravel : Return a 1-D tensor containing the elements of the input tensor.

    Examples
    --------
    >>> import mars.tensor as mt

    >>> x = mt.arange(-2, 3)
    >>> x.execute()
    array([-2, -1,  0,  1,  2])
    >>> mt.flatnonzero(x).execute()
    array([0, 1, 3, 4])

    Use the indices of the non-zero elements as an index array to extract
    these elements:

    >>> x.ravel()[mt.flatnonzero(x)].execute()  # TODO(jisheng): accomplish this after fancy indexing is supported

    """
    from ..base import ravel

    return nonzero(ravel(a))[0]