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version 2.100.0

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Function std.random.dice

Rolls a dice with relative probabilities stored in proportions. Returns the index in proportions that was chosen.

{null} dice(Rng, Num)()
if (isNumeric!Num && isForwardRange!Rng);

size_t dice(R, Range) (
  ref R rnd,
  Range proportions
)
if (isForwardRange!Range && isNumeric!(ElementType!Range) && !isArray!Range);

size_t dice(Range) (
  Range proportions
)
if (isForwardRange!Range && isNumeric!(ElementType!Range) && !isArray!Range);

{null} dice(Num)()
if (isNumeric!Num);

Parameters

NameDescription
rnd (optional) random number generator to use; if not specified, defaults to rndGen
proportions forward range or list of individual values whose elements correspond to the probabilities with which to choose the corresponding index value

Returns

Random variate drawn from the index values [0, ... proportions.length - 1], with the probability of getting an individual index value i being proportional to proportions[i].

Example

auto x = dice(0.5, 0.5);   // x is 0 or 1 in equal proportions
auto y = dice(50, 50);     // y is 0 or 1 in equal proportions
auto z = dice(70, 20, 10); // z is 0 70% of the time, 1 20% of the time,
                           // and 2 10% of the time

Example

auto rnd = MinstdRand0(42);
auto z = rnd.dice(70, 20, 10);
writeln(z); // 0
z = rnd.dice(30, 20, 40, 10);
writeln(z); // 2

Example

auto rnd = Xorshift(123_456_789);
auto i = dice(rnd, 0.0, 100.0);
writeln(i); // 1
i = dice(rnd, 100.0, 0.0);
writeln(i); // 0

i = dice(100U, 0U);
writeln(i); // 0

Authors

Andrei Alexandrescu Masahiro Nakagawa (Xorshift random generator) Joseph Rushton Wakeling (Algorithm D for random sampling) Ilya Yaroshenko (Mersenne Twister implementation, adapted from mir-random)

License

Boost License 1.0.