Shuffle Text File Delphi Source or anything else

Question

I have a stringlist with 10,000 entries. I have a shuffle routine, but accessing any of the items is taking a lot of time. Going through all 10k items takes a huge amount of time.

I want to save it do disk and then do a shuffle on the file using another method.

Any suggestions?

Answer 1

How is your shuffle-routine implemented? Especially the exchange-routine? If you have written your own, along these lines:

vTempSrting := vStringList[I]; 
vStringList.Delete(I); 
vStringList.Insert(J,vTempString);

it will be very slow. Use the exchange-method on the stringlist.

This code took 78 ms on my pretty average (3 year old) computer:

program Project1;

{$APPTYPE CONSOLE}

uses
  SysUtils,Classes,uIntegerList,Windows,Math;

procedure Shuffle(aSL : TStringList);
var I,J : integer;
begin
  for I := 0 to aSL.Count-1 do
  begin
    J := randomrange(I,aSL.Count);
    aSL.Exchange(I,J);
  end;
end;

procedure CreateTestFile;
var
  vSL : TStringList;
  I : integer;
begin
  vSL := TStringList.Create;
  try
    for I := 1 to 100000 do vSL.Add('Sample text #'+inttostr(I));
    vSL.SaveToFile('c:\test.txt');
  finally
    vSL.Free;
  end;
end;

function TestShuffle : longword;
var
  vSL : TStringList;
  vTick0 : longword;
begin
  vSL := TStringList.Create;
  try
    vTick0 := gettickcount;
    vSL.LoadFromFile('c:\test.txt');
    Shuffle(vSL);
    vSL.SaveToFile('c:\test.txt');
    Result := gettickcount - vTick0;
  finally
    vSL.Free;
  end;
end;

begin
  CreateTestFile;
  writeln(TestShuffle,' ms');
  readln;
end.