Delphi : Sorted List

Question

I need to sort close to a 1,00,000 floating point entries in Delphi. I am new to Delphi and would like to know if there are any ready made solutions available. I tried a few language provided constructs and they take an inordinate amount of time to run to completion.(a 5-10 sec execution time is fine for the application)

Answer 1

What version are you using? If you're in Delphi 2009 or 2010, you can use generics to make a TList<real> and call its Sort method.

If you're in an earlier version, the non-generic TList has a Sort method too, but it's a bit trickier to set up since it uses pointers, and Real (or Double), which is what you probably want to use as a floating point number, is too large to cast to a pointer.

Answer 2

why not just implement a quick Sort algorithm?

see this simple code

program ProjectSortFoat;

{$APPTYPE CONSOLE}

uses
  SysUtils;

procedure QuickSort(var List: array of Double; iLo, iHi: Integer) ;
var
  Lo       : integer;
  Hi       : integer;
  T        : Double;
  Mid      : Double;
begin
  Lo := iLo;
  Hi := iHi;
  Mid:= List[(Lo + Hi) div 2];
  repeat

    while List[Lo] < Mid do Inc(Lo) ;
    while List[Hi] > Mid do Dec(Hi) ;

    if Lo <= Hi then
    begin
      T := List[Lo];
      List[Lo] := List[Hi];
      List[Hi] := T;
      Inc(Lo);
      Dec(Hi);
    end;

  until Lo > Hi;

  if Hi > iLo then QuickSort(List, iLo, Hi);
  if Lo < iHi then QuickSort(List, Lo, iHi);

end;



const
Elements = 1000000;
var
  doubleArray : array of Double;
  i           : integer;
  t           : TDateTime;
begin
  SetLength(doubleArray,Elements);
  try
    t:=Now;
    Writeln('Init Generating '+FormatFloat('#,',Elements)+' random numbers ');
    for i:=low(doubleArray) to high(doubleArray) do
    doubleArray[i]:=Random(10000000)+Random; //can be improved
    Writeln('Elapsed '+FormatDateTime('HH:NN:SS.ZZZ',Now-t));

    t:=Now;
    Writeln('Sorting '+FormatFloat('#,',Elements)+' random numbers ');
    QuickSort(doubleArray, Low(doubleArray), High(doubleArray)) ;
    Writeln('Elapsed '+FormatDateTime('HH:NN:SS.ZZZ',Now-t));

  finally
  Finalize(doubleArray);
  end;
  Readln;
end.

in my machine, the execution time for sorting 1.000.000 float numbers is 0.167 seconds.

if you have delphi 7 or another older version (i don't know if exist in the new versions) you can check the

C:\Program Files\Borland\Delphi7\Demos\Threads

path, for a cool demo app using differents sorting algorithms an threads.