Re: Why no for table-iterator like e. g. "hashpairs"?

[nobody <nobody+lua-list@...>]

On 01/11/2019 09.55, bil til wrote:
> I assume quite often a very long listed/indexed table might have 
> additionally some further key-value pairs with "hash-keys". E. g. a 
> polyline/xy-curve with very many points might additionally have a 
> name field and maybe some further info fields.
>
> If I want to iterate over such "further info fields" in a fast way in
> lua (and I do NOT know the key names, or I possibly would like to 
> check such "further key names"), do I really have to iterate over the
> complete table with pairs? (is this not a complete waste of time, as
> I then possibly get also all the ipairs entries of the table for 
> iteration in my for loop?).

If you want to iterate over different collections of fields, use
multiple tables and put the <LOTS of stuff that you only want SOMETIMES>
into a separate table.  Then you can iterate quickly over either the
list or the extra fields.  E.g.:

  curve = { { 23, 42 }, { 21, 37 }, metadata = { input = "mouse" } }

[ipairs gets you just the list, pairs on .metadata is the other fields]

or

  curve = { input = "mouse", data = { { 23, 42 }, { 21, 37 }, … }, … }

[tradeoff: different order, there's ONLY data in .data, but you'll have
to manually skip .data when doing pairs() on the outer container.]

or maybe even

  curve = { input = "mouse", x = { 23, 21, … }, y = { 42, 37, … }, … }

[split/"planar" representation tends to save A LOT of memory, if your
code can handle it]

(See also http://lua-users.org/lists/lua-l/2016-08/msg00256.html for
some more bad ideas.)

-- nobody