Samples and permutations

From Free Pascal wiki

Functions for samples and permutations deliver randomly ordered vectors of data. Random samples may be used for very diverse applications, including simulating rolls of a die, generating anonymised IDs (e.g. for clinical trials), Monte Carlo simulations and wide-range statistical applications.

The following function delivers a vector of longint values, which are randomly ordered and range from min to max:

type
  TLongintvector_data = array of longint;   

function sample(min, max: longint; replace: boolean): TLongintvector_data;
var
  i, j, num1, num2: longint;
  Vector1, Vector2: TLongintvector_data;
begin
  randomize;                        // initialise random number generator
  num1 := 1 + max - min;            // length of vector to be generated
  SetLength(Vector1, num1);         // vector for original (ordered) data
  SetLength(Vector2, num1);         // vector with permuted data
  if num1 > 0 then
  begin
    for i := 0 to num1 - 1 do
    begin                           
      Vector1[i] := min + i;        // initialise original vector
    end;
    num2 := num1;
    for i := 1 to num1 do
    begin
      j := random(num2);            // select random element of Vector1
      Vector2[i - 1] := Vector1[j]; // and assign to next element of Vector2
      if not replace then
      begin
        Delete(Vector1, j, 1);      // remove randomly selected element
        Dec(num2);                  // and adapt size
      end;
    end;
  end;
  result := Vector2;
end;

Depending on the value of the parameter replace, the random elements of the vector are provided with or without replacement. With replacement, one number may occur several times. Without replacement all elements of the vector will contain unique numbers.

See also