PureBasic Forums - English

Posted: **Mon Jul 27, 2009 12:11 am**

Hello!

What do you think of the idea to implement the possibility for a callback for all the sorting commands in order to allow the coder to use its own order?

Example:

Code: Select all

Procedure callback(a, b)
	; your own algorithm goes here
	If a < b
		ProcedureReturn #PB_String_Lower ; -1
	ElseIf a = b
		ProcedureReturn #PB_String_Equal ; 0
	Else
		ProcedureReturn #PB_String_Greater ; 1
	EndIf
EndProcedure

SortList(myList(), #PB_Sort_Ascending, @callback())

The callback should return -1, 0 or 1 for lower, equal or greater results.
The new syntax for SortList(), for example could be

Code: Select all

SortList(ListName(), Options [, @Callback() [, Start, End]])

Whereas it could be 0 to leave it out while using Start/End scope.

Posted: **Mon Jul 27, 2009 12:21 pm**

Yes, it would be nice. I have implemented it this way in the quicksort routine I use. Obviously there is a little penalty in calling the compare procedure.
But personally I don't consider it a problem.

But I am a BIG fan of callback procedures in general.

Maybe there are sort routines like that in the forum too, I think I saw something of that kind here before.

Posted: **Tue Jul 28, 2009 3:57 am**

> Obviously there is a little penalty in calling the compare procedure
There will be a little penalty, because you need a few steps to call the procedure; but most of the time is being spent on the algorithm of the coder. Not matter how efficient he/she will code, it will take a certain amount of time.

It would be interesting to hear, which algorithm PB uses to sort the content. Can you tell us, PB team? I can imagine, that there are algorithms that are efficient, but need much less steps than other algorithms.
In other words: the less steps the internal sorting algorithm needs, the more time can be spent on the callback; the time needed will be the same as using no callback and an algorithm that takes more steps.
Hope, you could follow me.

> But personally I don't consider it a problem
Me too. PackMemory(), for example, also accepts callbacks. I bet, a callback there also creates a little penalty, however, you would never get the idea that the (de)compressions takes much more time, just because of the callback.

> Maybe there are sort routines like that in the forum too
Well, it would be neat to have this natively implemented.

That's the reason for posting it into the feature request subforum. If we always take any codes from the forum, we could close the feature request subforum.

Posted: **Tue Jul 28, 2009 12:00 pm**

AND51 wrote:It would be interesting to hear, which algorithm PB uses to sort the content. Can you tell us, PB team? I can imagine, that there are algorithms that are efficient, but need much less steps than other algorithms.

Iirc, PB 4.3x uses Mergesort for SortStructuredList() / SortList() and Quicksort for SortArray().

Posted: **Tue Jul 28, 2009 3:00 pm**

Cool, thanks. I'll google them to read their description.
By the way: to be honest, this feature request was empowered by your PureLVSORT library, where you can also set a custom callback for sorting a ListIconGadget().

PureBasic Forums - English

Callback for Sorting-commands to allow custom sorting orders

Callback for Sorting-commands to allow custom sorting orders