[capink]

Since this is an old thread that predates the introduction of python templates by chaley, here is the python equivalent for the chaley's GPM template:

python:
def evaluate(book, context):
    vals = context.globals.get('highest_index_ids')
    if not vals:
        vals = context.globals['highest_index_ids'] = []
        db = context.db
        cats = db.new_api.get_categories(book_ids=None)
        all_series = [ t.name for t in cats['series'] ]
        for series in all_series:
            book_ids = db.data.search_getting_ids(f'series:"={series}"', '')
            indices = {}
            for book_id in book_ids:
                idx = db.new_api.field_for('series_index', book_id)
                indices[idx] = book_id
            vals.append(indices[max(indices.keys())])
    return '1' if book.id in vals else '0'

This should be a little faster.