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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _slice_data(self, source_area, slices, dataset):
 """Slice the data to reduce it."""

        slice_x, slice_y = slices
        dataset = dataset.isel(x=slice_x, y=slice_y)
        assert ('x', source_area.x_size) in dataset.sizes.items()
        assert ('y', source_area.y_size) in dataset.sizes.items()
        dataset.attrs['area'] = source_area

        return dataset