[capink]

Originally Posted by chaley

This example action computes the average rating for 3 Genres and their children then stores those ratings in a tags-like custom column in the form 'genre name':average_rating.

Nice work.

Originally Posted by chaley

@capink:I couldn't get the mean() function to work. How do I convert the result of "from_search()" to an "iterable"?

I don't know what exactly is happening. But removing the spaces in the genres like below, makes it work. Will investigate this later:

This is working for me:

program:
	genres = 'Comics,Mysteries,Science Fiction';
	res = '';
	for g in genres:
		ratings = from_search('rating', strcat('#genre:"=.', g, '"'));
		avg = mean(ratings);
		res = list_union(res, strcat(g, ':', avg), ',')
	rof;
	res

Notice that mean discards any non numerical value. If someone wants None values to weigh on the average, modify as follows:

program:
	genres = 'Comics,Mysteries,Science Fiction';
	res = '';
	for g in genres:
		ratings = from_search('rating', strcat('#genre:"=.', g, '"'));
		ratings = re_non_numerical(ratings, 0);
		avg = mean(ratings);
		res = list_union(res, strcat(g, ':', avg), ',')
	rof;
	res

Also there is a bug with the mean function when it is fed an empty list or a list that contains no numerical values. Will fix this in the next release.

Originally Posted by chaley

My concern is "mysterious behavior" that depends on a sequence of choices. I am not convinced that action A should affect action B. If it does then there should be something that explicitly declares "action global" variables that persist. Or perhaps the notion of "super actions" that run named actions in a sequence using the same globals dict.

The next question is their lifetime. Do they live for the calibre invocation, while a library is open, while a VL is open, or something else?

That makes sense. Will leave it as it is for now. Maybe in the future will add a template function to let the user persist whatever he wants.

Edit1: No need to create a template function for that. If a user wants to persist data, he can create an empty book record and use the single field edit to persist data to it.

Edit2: from_search() and from_selection() always return an iterable (comma separated values).