std::experimental::sample
Defined in header <experimental/algorithm>


template< class PopulationIterator, class SampleIterator, class Distance, class URBG > 
(1)  (library fundamentals TS) 
template< class PopulationIterator, class SampleIterator, class Distance > SampleIterator sample( PopulationIterator first, PopulationIterator last, 
(2)  (library fundamentals TS v2) 
Selects n
elements from the sequence [first; last) such that each possible sample has equal probability of appearance, and writes those selected elements into the output iterator out
If n
is greater than the number of elements in the sequence, selects lastfirst elements.
The algorithm is stable only if PopulationIterator
meets the requirements of LegacyForwardIterator
g
.Parameters
first, last    pair of iterators forming the range from which to make the sampling (the population) 
out    the output iterator where the samples are written. Must not be in the [first;last) range 
n    number of samples to make 
g    the random number generator used as the source of randomness 
PopulationIterator must meet the requirements of LegacyInputIterator.
 
SampleIterator must meet the requirements of LegacyOutputIterator.
 
SampleIterator must also meet the requirements of LegacyRandomAccessIterator if PopulationIterator doesn't meet LegacyForwardIterator
 
PopulationIterator 's value type must be writeable to out
 
Distance must be an integer type
 
URBG must meet the requirements of UniformRandomBitGenerator and its return type must be convertible to Distance

Return value
Returns a copy of out
after the last sample that was output, that is, end of the sample range.
Complexity
Linear in std::distance(first,last)
Notes
This function may implement selection sampling or reservoir sampling.
Example
#include <iostream> #include <random> #include <string> #include <iterator> #include <experimental/algorithm> int main() { std::string in = "abcdefgh", out; std::experimental::sample(in.begin(), in.end(), std::back_inserter(out), 5, std::mt19937{std::random_device{}()}); std::cout << "five random letters out of " << in << " : " << out << '\n'; }
Possible output:
five random letters out of abcdefgh : cdefg
See also
(until C++17)(C++11) 
randomly reorders elements in a range (function template) 