Samples and permutations: what changed
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Title: Samples and permutations
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| 1 | + | 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. | |
| 2 | + | ||
| 3 | + | The following function delivers a vector of **longint** values, which are randomly ordered and range from **min** to **max**: | |
| 4 | + | ||
| 5 | + | ``` pascal | |
| 6 | + | type | |
| 7 | + | TLongintvector_data = array of longint; | |
| 8 | + | ||
| 9 | + | function sample(min, max: longint; replace: boolean): TLongintvector_data; | |
| 10 | + | var | |
| 11 | + | i, j, num1, num2: longint; | |
| 12 | + | Vector1, Vector2: TLongintvector_data; | |
| 13 | + | begin | |
| 14 | + | randomize; // initialise random number generator | |
| 15 | + | num1 := 1 + max - min; // length of vector to be generated | |
| 16 | + | SetLength(Vector1, num1); // vector for original (ordered) data | |
| 17 | + | SetLength(Vector2, num1); // vector with permuted data | |
| 18 | + | if num1 > 0 then | |
| 19 | + | begin | |
| 20 | + | for i := 0 to num1 - 1 do | |
| 21 | + | begin | |
| 22 | + | Vector1[i] := min + i; // initialise original vector | |
| 23 | + | end; | |
| 24 | + | num2 := num1; | |
| 25 | + | for i := 1 to num1 do | |
| 26 | + | begin | |
| 27 | + | j := random(num2); // select random element of Vector1 | |
| 28 | + | Vector2[i - 1] := Vector1[j]; // and assign to next element of Vector2 | |
| 29 | + | if not replace then | |
| 30 | + | begin | |
| 31 | + | Delete(Vector1, j, 1); // remove randomly selected element | |
| 32 | + | Dec(num2); // and adapt size | |
| 33 | + | end; | |
| 34 | + | end; | |
| 35 | + | end; | |
| 36 | + | result := Vector2; | |
| 37 | + | end; | |
| 38 | + | ``` | |
| 39 | + | ||
| 40 | + | 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. | |
| 41 | + | ||
| 42 | + | ## See also | |
| 43 | + | ||
| 44 | + | - [[Ranking vectors of data]] | |
| 45 | + | - [[Dev random]] | |
| 46 | + | - [[Functions for descriptive statistics]] | |
| 47 | + | - [[Generating Random Numbers]] | |
| 48 | + | - [[Marsaglia&|Marsaglia's pseudo random number generators]] | |
| 49 | + | - [[A simple implementation of the Mersenne twister]] | |
| 50 | + | - [[Delphi compatible LCG Random]] | |
| 51 | + | - [[EverettRandom]] | |
| 52 | + | ||
| 53 | + | --- | |
| 54 | + | *From the Free Pascal wiki, page "Samples and permutations", as it stood on 2021-03-06 after a change by Jwdietrich, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).* | |
| 55 | + | Category: Code | |
| 56 | + | Category: Mathematics | |
| 57 | + | Category: Modelling and Simulation | |
| 58 | + | Category: Statistical algorithms |