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Function `std.random.partialShuffle`

Partially shuffles the elements of r such that upon returning r[0 .. n] is a random subset of r and is randomly ordered. r[n .. r.length] will contain the elements not in r[0 .. n]. These will be in an undefined order, but will not be random in the sense that their order after partialShuffle returns will not be independent of their order before partialShuffle was called.


						
				Range partialShuffle(Range, RandomGen)
				(
				

				  Range r,
				

				  in size_t n,
				

				  ref RandomGen gen
				

				)
				

				if (isRandomAccessRange!Range && isUniformRNG!RandomGen);
				

				

				Range partialShuffle(Range)
				(
				

				  Range r,
				

				  in size_t n
				

				)
				

				if (isRandomAccessRange!Range);

r must be a random-access range with length. n must be less than or equal to r.length. If no RNG is specified, rndGen will be used.

Parameters

Name	Description
r	random-access range whose elements are to be shuffled
n	number of elements of `r` to shuffle (counting from the beginning); must be less than `r.length`
gen	(optional) random number generator to use; if not specified, defaults to `rndGen`

Returns

The shuffled random-access range.

Example

auto rnd = MinstdRand0(42);

auto arr = [1, 2, 3, 4, 5, 6];
arr = arr.dup.partialShuffle(1, rnd);

version(X86_64) // Issue 15147
assert(arr == [2, 1, 3, 4, 5, 6]); // 1<->2

arr = arr.dup.partialShuffle(2, rnd);
version(X86_64) // Issue 15147
assert(arr == [1, 4, 3, 2, 5, 6]); // 1<->2, 2<->4

arr = arr.dup.partialShuffle(3, rnd);
version(X86_64) // Issue 15147
assert(arr == [5, 4, 6, 2, 1, 3]); // 1<->5, 2<->4, 3<->6

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.