help with custom column

[Noughty]

Basically I am trying to make a list of tags, #shelf (merge these two) and remove all values which are in #genre, #character, #legth.

I have been trying to make it on my own half successfully. I tried list_differences

{#shelf:'list_difference(list_union(field('tags'), field('#shelf'), ','), list_union(list_union(field('#genre'), field('#length'), ','), field('#character'), ','),',')'}

Apparently the beginning

{#shelf:

does nothing but if I remove it, it stops working. How do I need to edit it to make it correct? Now it does the job, but I think it's a little incorrect. Might get wrong results or something.

Are there any other mistakes?

And keep in mind that I don't even know how I managed to do this much . That's my most complicated creation for calibre.

[chaley]

As for your first question, you can use "{:" instead of "{#shelf:".

Your template seems to do what you want. However, the performance will be less than ideal. This is a case where you should use a custom template function, which will be at least 100 times faster. However, that would require you to write the function in python using calibre's template function editor (preferences -> template functions), which you might not be prepared to do.

[Noughty]

Thanks. After all day dealing with templates I will dream them for sure. I don't even want to think of python.

Thanks for clearing that up. I fixed it up.

[chaley]

Just for fun, I wrote the custom template function to do this job.

Function name: myListMerge (or whatever you want)
Argument count: 5
Program code:
def evaluate(self, formatter, kwargs, mi, locals, tags, shelf, genre, length, character):
	r = set([t.strip() for t in tags.split(',') if t.strip()])
	r |= set([t.strip() for t in shelf.split(',') if t.strip()])
	r -= set([t.strip() for t in genre.split(',') if t.strip()])
	r -= set([t.strip() for t in length.split(',') if t.strip()])
	r -= set([t.strip() for t in character.split(',') if t.strip()])
	return ', '.join(sorted(r))

You would use it like

{:'myListMerge(field('tags'), field('#shelf'), field('#genre'), field('#length'), field('#character'))'}

In fact, I don't suggest that you use it unless you understand it, otherwise you won't be able to maintain it. I did it because I was curious.

[Noughty]

Who knows maybe one day I get that too. Now I am starting to actually understand templates and how to use them. Once you get the "grammar" all you need is to find the function which does what you want.

My previous result was messy so I edited it:

{:'list_sort(list_difference(list_union(field('#shelf'), field('tags'), ','), list_union(list_union(field('#genre'), field('#length'), ','), field('#character'), ','),','),0,',')'}

Returns me a nice alphabetical list of all tags, shelves which aren't categorized into separate lists. And I can easily edit it for new categories etc.