[chaley]

Originally Posted by dunhill

I have a custom information column with this template, maybe you can adapt it and see if it works for you.
[...]

That is an excellent start.

Here is the converted template. It returns the maximum series index for the series of the book. Somehow the indenting was lost in @dunhill's post, which is corrected here.

python:
def evaluate(book, context):
	db = context.db.new_api
	# Count the books in the series. First get the series name
	series = book.get('series')
	if series:
		# The book is in a series. Get all the books in that series
		series_id = db.get_item_id('series', series, case_sensitive=True)
		books = db.books_for_field('series', series_id)
		# Get the highest series index
		max_dex = -9999
		for b in books:
			ser = db.field_for('series_index', b)
			if ser > max_dex:
				max_dex = ser
		# Convert the max index to a string.
		x = str(int(max_dex) if max_dex.is_integer() else max_dex)
	else:
		x = ''
	return x

This template could be used in a custom column but it might be too slow because it operates on all the books all the time. It can be used on demand in Action chains, possibly in a Single Field Edit action that operates on all the books in a series.