def fill_feature_group_definition(config):
    """
    If feature_group_definition is not presents, this function sets it to all
    the distinct feature_aggregations' prefixes

    Args:
        config (dict) a triage experiment configuration

    Returns: (dict) a triage feature_group config
    """
    feature_group_definition = config.get('feature_group_definition', {})
    if not feature_group_definition:
        feature_aggregations = config['feature_aggregations']

        feature_group_definition['prefix'] = list({agg['prefix'] for agg in feature_aggregations})

    return feature_group_definition