Sort authors via last name in Tiddlywiki - tiddlywiki

Question

It would be good to sort lists using an author's last name.
I have this code in one of the tiddlers, it lists all the tiddlers tagged 'author' and sorts alphabetically:
<$list filter='[tag[author]sort[title]]'>
</$list>
e.g.
Adam Robinson
Andrew Adonis
Benjamin Franklin
Dale Carnegie
Daniel Priestley
George Leonard
I would like the list to be sorted by last name, so it looks like this:
Adonis, Andrew
Carnegie, Dale
Franklin, Benjamin
Leonard, George
Priestley, Daniel
Robinson, Adam
Any ideas how to do this?

Answer 1

Easy option: Add a ByLastName field populated the way you want and sort on that.
Medium option: Introduce the notion of generated fields into tiddlywiki.
Hard option: Modify the sort filter to call a macro with whatever data you specify and then sort the original list based on the result.

Answer 2

In recent versions of TiddlyWiki, you can do this with the sortsub operator, which sorts based on the results of applying a filter expression to the inputs. Note that when you use this operator (or any other operator that takes a subfilter), you have to define the subfilter using a macro, or there's no way for TiddlyWiki to tell which square brackets are part of the main filter and which are part of the subfilter.
Here's a minimal working version:
\define myfilt() [split[ ]last[]]
<$list filter="[tag[author]sortsub<myfilt>]">
...
</$list>
To get the display to show up as "Lastname, Firstname", as in your example, rather than just showing the title of the tiddler as is:
\define myfilt() [split[ ]last[]]
<$list filter="[tag[author]sortsub<myfilt>]">
<$set name=formattedName value={{{ [all[current]split[ ]last[]addsuffix[, ]] [all[current]split[ ]butlast[]] +[join[]] }}}>
<$link to=<<currentTiddler>>><<formattedName>></$link><br>
</$set>
</$list>
We calculate the new format using a filter in {{{ triple curly braces }}} and assign it to a variable (note the use of butlast[] rather than first[] so that if someone has more than two names, the middle ones go on the end rather than disappearing). Then we create a link whose text is that new formatted version, and whose target is the original tiddler name.