Roll

Template:Primitive is a monadic scalar function which returns random or pseudo-random numbers. Each scalar in the argument must be a non-negative integer. If it is a positive number n, then Roll chooses one of the first n indices. In some dialects Roll chooses a floating-point number between 0 and 1 when the argument has a zero.

Examples

      ? 4 ⍴ 6                   ⍝ Roll four six-sided dice
1 4 1 1
      ? 3 2 1 0                 ⍝ The result for 1 is always 1
2 2 1 0.9637543707
      {⍵[?8⍴≢⍵]} 'Hello'        ⍝ Choose 8 random letters
eeHHHolo

Works in: Dyalog APL, dzaima/APL

Description

Each scalar in the argument to Roll must be a non-negative integer.

The result of Roll on each number n is either

• A real number chosen uniformly at random from between 0 and 1, if n is 0; or
• One of the elements of ⍳n chosen uniformly at random, otherwise.

Because Iota depends on index origin, Roll depends on index origin unless every number in the argument is 0.

The choices made by Roll do not have to be truly random: they may be pseudorandom (generated by a deterministic but difficult to predict algorithm) or taken from the operating system. They way random numbers are generated is controlled by the random link ⎕RL.

External links

Lessons

APL Cultivation

Documentation

Dyalog

APLX

J Dictionary, NuVoc