How to sort only a part of a list

[caymon 0]

I have a list of objects, declared like TMyList = class(TObjectList<T>) with say  1000 elements.

The list is sorted according to a certain comparer.

 

Then, how do I sort again, but only the first 100 elements of that list, according to another comparer.

 

The construction MyList.Sort(...) doesn't allow to specify a low and a high bound of the sort.

[Fr0sT.Brutal 900]

If speed is not critical, you can determine the index of each object from inside comparer callback via IndexOf

[Uwe Raabe 2063]

You didn't mention the Delphi version, but since Delphi 11 you can use the appropriate Sort overload taking a comparer, start index and count.

procedure Sort; overload;
procedure Sort(const AComparer: IComparer<T>); overload;
procedure Sort(const AComparer: IComparer<T>; Index, Count: Integer); overload;

 

[caymon 0]

Thank you for the info about Delphi 11.

Indeed, I have that version but the program that needs the change (600K lines) was compiled using 10.4.

However, I've checked that it also compiles (and seems to run) properly using 11, maybe it is time to switch!

[Stefan Glienke 2016]

Using 10.4 you can do this with the following code:

  TArray.Sort<yourtype>(list.PList^, list.Comparer, index, count);