def populateCategoriesOut(self, categories, output):
if categories[<NUM_LIT:0>] is None:<EOL><INDENT>output[:] = -<NUM_LIT:1><EOL><DEDENT>else:<EOL><INDENT>for i, cat in enumerate(categories[:len(output)]):<EOL><INDENT>output[i] = cat<EOL><DEDENT>output[len(categories):] = -<NUM_LIT:1><EOL><DEDENT>
Populate the output array with the category indices.

.. note:: Non-categories are represented with ``-1``.

:param categories: (list) of category strings
:param output: (list) category output, will be overwritten