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Attila Kovacs

Generic set comparer

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Is there a mature library for generic (multi)set operations?

 

(Edit: Reading my topic, i meant mathematical sets, maybe I could name it List instead of set, the result what counts)

 

I'd imagine that working like this:

 

unit xyz.sets;

interface

uses
  System.Generics.Defaults;

type
  TSets<T> = class
  public type
    TSet = class
    private
      FValues: TArray<T>;
    public
      procedure Add(AValue: T);
    end;
  private
  var
    FSets: TArray<TSet>;
    FComparer: IEqualityComparer<T>;
  public
    constructor Create;
    function AddSet: TSet;
    function GetIntersection(ASets: array of TSet): TArray<T>;
    property Comparer: IEqualityComparer<T> read FComparer write FComparer;
  end;

implementation

uses
  System.SysUtils;

{ TSets<T> }

function TSets<T>.AddSet: TSet;
var
  l: integer;
begin
  Result := TSet.Create;
  l := Length(FSets);
  SetLength(FSets, l + 1);
  FSets[l] := Result;
end;

{ TSets<T>.TSet }

procedure TSets<T>.TSet.Add(AValue: T);
var
  l: integer;
begin
  l := Length(FValues);
  SetLength(FValues, l + 1);
  FValues[l] := AValue;
end;


constructor TSets<T>.Create;
begin
  FComparer := TEqualityComparer<T>.Default;
end;

// O(n^x)
function TSets<T>.GetIntersection(ASets: array of TSet): TArray<T>;
var
  i, j, k, l: integer;
begin
  if FComparer = nil then
    raise Exception.Create('No comparer defined.');
  if Length(ASets) > 1 then
  begin
    for i := 0 to High(ASets[0].FValues) do
      for j := 1 to High(ASets) do
        for k := 0 to High(ASets[j].FValues) do
          if FComparer.Equals(ASets[0].FValues[i], ASets[j].FValues[k]) then
          begin
            l := Length(Result);
            SetLength(Result, l + 1);
            Result[l] := ASets[0].FValues[i];
          end;
  end
  else
    Result := ASets[0].FValues;
end;

end.

------  ------  ------  ------  ------  ------  ------  ------  ------

program Project1;

{$APPTYPE CONSOLE}
{$R *.res}

uses
  System.SysUtils,
  xyz.sets in 'xyz.sets.pas';

var
  rp: procedure;

  i: integer;
  sets: TSets<string>;
  set1, set2: TSets<string>.TSet;
  res: TArray<string>;


procedure x;
begin
  ExitProcessProc := rp;
  ReadLn;
end;


begin
  ReportMemoryLeaksOnShutdown := True;
  rp := ExitProcessProc;
  ExitProcessProc := x;

  sets := TSets<string>.Create;
  set1 := sets.AddSet;
  set2 := sets.AddSet;
  try
    set1.Add('hello');
    set1.Add('leo');

    set2.Add('hello');
    set2.Add('bello');

    res := sets.GetIntersection([set1, set2]);
    for i := 0 to High(res) do
      WriteLn(res[i]);

  finally
    set1.Free;
    set2.Free;
    sets.Free;
  end;

end.

 

Edited by Attila Kovacs

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Not aware of any library, but I have written small routines like

  function AnyOf(ATarget, AActual: TOptionSet): Boolean;  and

  function Contains(ATarget, AActual: TOptionSet): Boolean;  

 

Makes the code more readable, I think, which is all I really needed. My notion was that although the set operations are pretty terse, not a lot of devs spend much time reading them, so comprehension may be a struggle. AnyOf() handles any members of the target being present in the actual:

    Result := ATarget * AActual <> [];

while Contains() tests:

    Result := ATarget * AActual = ATarget;

 

Unless your need is for a lot of densely coded operations, this kind of thing may be sufficient. If you do need dense code, then you may better simply use the existing operators.

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Ahm, i was afraid that using the word "set" would be misleading, and I was right, sorry, but lists are a bit different from multisets again, so I don't know,

I need to compare two or more "set of anything" and I'm tired writing it always manually.

 

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24 minutes ago, Attila Kovacs said:

Ahm, i was afraid that using the word "set" would be misleading, and I was right, sorry, but lists are a bit different from multisets again, so I don't know,

I need to compare two or more "set of anything" and I'm tired writing it always manually.

 

Ah, I did indeed misunderstand. So really, you want set operations on collections of whatever type. 

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2 hours ago, Attila Kovacs said:

@Leif Uneus Wow, thanks a lot, and also to LU RD if he ever reads this.

Well. there is no secret that LU RD is short for Leif Uneus R&D Manager of Opsis AB, a company that provides analysers and software for industrial and environmental analysis of gases and particulates.

A company started 36 years ago by me and my business partner.

 

Core software in the analysers is built with Turbo Pascal 7. Delphi is a tool for our software for data management, analysis and reporting.

Edited by Leif Uneus
  • Like 1

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Can we please sit for a while and appreciate how cute the separating line with scissors is

  • Haha 3

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