std.random.RandomCover/randomCover - multiple declarations
Function randomCover
Covers a given range r in a random manner, i.e. goes through each
element of r once and only once, just in a random order. r
must be a random-access range with length.
auto auto randomCover(Range, UniformRNG)
(
Range r,
auto ref UniformRNG rng
)
if (isRandomAccessRange!Range && isUniformRNG!UniformRNG);
auto auto randomCover(Range)
(
Range r
)
if (isRandomAccessRange!Range);
If no random number generator is passed to randomCover, the
thread-global RNG rndGen will be used internally.
Parameters
| Name | Description |
|---|---|
| r | random-access range to cover |
| rng | (optional) random number generator to use;
if not specified, defaults to rndGen |
Returns
Range whose elements consist of the elements of r,
in random order. Will be a forward range if both r and
rng are forward ranges, an input range otherwise.
Example
int[] a = [ 0, 1, 2, 3, 4, 5, 6, 7, 8 ];
foreach (e; randomCover(a))
{
writeln(e);
}WARNING: If an alternative RNG is desired, it is essential for this to be a new RNG seeded in an unpredictable manner. Passing it a RNG used elsewhere in the program will result in unintended correlations, due to the current implementation of RNGs as value types.
Example
int[] a = [ 0, 1, 2, 3, 4, 5, 6, 7, 8 ];
foreach (e; randomCover(a, Random(unpredictableSeed))) // correct!
{
writeln(e);
}
foreach (e; randomCover(a, rndGen)) // DANGEROUS!! rndGen gets copied by value
{
writeln(e);
}
foreach (e; randomCover(a, rndGen)) // ... so this second random cover
{ // will output the same sequence as
writeln(e); // the previous one.
}Struct RandomCover
Covers a given range r in a random manner, i.e. goes through each
element of r once and only once, just in a random order. r
must be a random-access range with length.
struct RandomCover(Range, UniformRNG)
if (isRandomAccessRange!Range && (isUniformRNG!UniformRNG || is(UniformRNG == void)));
If no random number generator is passed to randomCover, the
thread-global RNG rndGen will be used internally.
Parameters
| Name | Description |
|---|---|
| r | random-access range to cover |
| rng | (optional) random number generator to use;
if not specified, defaults to rndGen |
Returns
Range whose elements consist of the elements of r,
in random order. Will be a forward range if both r and
rng are forward ranges, an input range otherwise.
Example
int[] a = [ 0, 1, 2, 3, 4, 5, 6, 7, 8 ];
foreach (e; randomCover(a))
{
writeln(e);
}WARNING: If an alternative RNG is desired, it is essential for this to be a new RNG seeded in an unpredictable manner. Passing it a RNG used elsewhere in the program will result in unintended correlations, due to the current implementation of RNGs as value types.
Example
int[] a = [ 0, 1, 2, 3, 4, 5, 6, 7, 8 ];
foreach (e; randomCover(a, Random(unpredictableSeed))) // correct!
{
writeln(e);
}
foreach (e; randomCover(a, rndGen)) // DANGEROUS!! rndGen gets copied by value
{
writeln(e);
}
foreach (e; randomCover(a, rndGen)) // ... so this second random cover
{ // will output the same sequence as
writeln(e); // the previous one.
}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)