[TIP] Sorting by ValueList and synchronized sorting

[Richard Gaskin]

J. Landman Gay wrote:

> Richard Gaskin wrote:
>> 
>> 1. Using a function for a sortKey expression introduces a "sometimes" 
>> rule in terms of understanding the order of expression evaluation in the 
>> engine, in which most of the time functions are evaluated first but in 
>> this case the function is applied repeatedly for each line of the sort 
>> container as the sort command is run.
> 
> Well, not really. It's more like a substitution for what the engine does 
> anyway. When the engine sorts a container, it has to assign a position 
> for each element being sorted. A custom sort function does the same 
> thing; the engine will use the number returned by the function when 
> arranging the elements.
> 
> The order of evaluation hasn't changed, and functions are still 
> evaluated first. But when sorting, each element has to be evaluated 
> individually.

Right.  That's what initially threw me.

As far as I can recall, this optional form of the sort command is the 
only way to call a function iteratively without using a repeat loop.

Are there others I've forgotten?

It's very handy, but a cognitive hurdle for me at first.  I'd never seen 
anything like it before.

Anyone else have a mental hiccup when they first encountered this?

-- 
  Richard Gaskin
  Managing Editor, revJournal
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