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            __PACKAGE__->_crop_assign(
                $ret, $arr, 
                { 
                    out => $ret,
                    begin => $begin,
                    end => $end
                }
            );
        }
        $idx += $arr->shape->[$axis];
    }
    return $ret
}

=head2 arange

    Similar function in the MXNet ndarray as numpy.arange
    See Also https://docs.scipy.org/doc/numpy/reference/generated/numpy.arange.html.

    Parameters
    ----------
    :$start=0 : number, optional
        Start of interval. The interval includes this value. The default start value is 0.
    $stop= : number, optional
        End of interval. The interval does not include this value.
    :$step=1 : number, optional
        Spacing between the values
    :$repeat=1 : number, optional
        The repeating time of all elements.
        E.g repeat=3, the element a will be repeated three times --> a, a, a.
    :$ctx : Context, optional
        The context of the NDArray, defaultw to current default context.
    :$dtype : data type, optional
        The value type of the NDArray, defaults to float32

    Returns
    -------
    $out : NDArray
        The created NDArray
=cut

method arange(Index :$start=0, Index :$stop=, Index :$step=1, Index :$repeat=1,
              AI::MXNet::Context :$ctx=AI::MXNet::Context->current_ctx, Dtype :$dtype='float32')
{
    return __PACKAGE__->_arange({
                start => $start,
                (defined $stop ? (stop => $stop) : ()),
                step => $step,
                repeat => $repeat,
                dtype => $dtype,
                ctx => "$ctx"
    });
}

=head2 load

    Loads ndarrays from a binary file.

    You can also use Storable to do the job if you only work with Perl.
    The advantage of load/save is the file is language agnostic.
    This means the file saved using save can be loaded by other language binding of mxnet.
    You also get the benefit being able to directly load/save from cloud storage(S3, HDFS)

    Parameters
    ----------
    fname : str
        The name of the file.Can be S3 or HDFS address (remember built with S3 support).
        Example of fname:

        - `s3://my-bucket/path/my-s3-ndarray`
        - `hdfs://my-bucket/path/my-hdfs-ndarray`
        - `/path-to/my-local-ndarray`

    Returns
    -------
    $out : array ref of NDArrays or hash ref with NDArrays
=cut

method load(Str $filename)
{
    my ($handles, $names) = check_call(AI::MXNetCAPI::NDArrayLoad($filename));
    if (not @$names)
    {
        return [map { __PACKAGE__->new(handle => $_) } @$handles];
    }
    else
    {
        my $n = @$names;
        my $h = @$handles;
        confess("Handles [$h] and names [$n] count mismatch") unless $h == $n;
        my %ret;
        @ret{ @$names } = map { __PACKAGE__->new(handle => $_) } @$handles;
        return \%ret;
    }
}

=head2 save

    Save array ref of NDArray or hash of str->NDArray to a binary file.

    You can also use Storable to do the job if you only work with Perl.
    The advantage of load/save is the file is language agnostic.
    This means the file saved using save can be loaded by other language binding of mxnet.
    You also get the benefit being able to directly load/save from cloud storage(S3, HDFS)

    Parameters
    ----------
    fname : str
        The name of the file.Can be S3 or HDFS address (remember built with S3 support).
        Example of fname:

        - `s3://my-bucket/path/my-s3-ndarray`
        - `hdfs://my-bucket/path/my-hdfs-ndarray`
        - `/path-to/my-local-ndarray`

    $data : array ref of NDArrays or hash ref of NDArrays
        The data to be saved.
=cut

method save(Str $filename, ArrayRef[AI::MXNet::NDArray]|HashRef[AI::MXNet::NDArray] $data)
{
    my $handles = [];
    my $names = [];
    if(ref $data eq 'HASH')
    {
        for my $name (keys %$data)
        {
            push @$names, $name;
            push @$handles, $data->{ $name }->handle;
        }
    }
    else
    {
        @$handles = map { $_->handle } @$data;
    }
    check_call(
        AI::MXNetCAPI::NDArraySave(
            $filename,
            scalar(@$handles),
            $handles,
            $names
        )
    );
}

=head2 imdecode

    Decode an image from string. Requires OpenCV to work.

    Parameters
    ----------
    $str_img : str
        binary image data
    :$clip_rect : iterable of 4 int
        clip decoded image to rectangle (x0, y0, x1, y1)
    :$out= : Maybe[NDArray]
        output buffer. can be 3 dimensional (c, h, w) or 4 dimensional (n, c, h, w)
    :$index : int
        output decoded image to i-th slice of 4 dimensional buffer
    :$channels=3 : int
        number of channels to output. Decode to grey scale when channels = 1.
    $mean= : Maybe[NDArray]
        subtract mean from decode image before outputting.