Difference between revisions of "cpp/algorithm/sample"
m (more random-looking example output (obtained from clang)) |
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If {{tt|n}} is greater than the number of elements in the sequence, selects {{c|last-first}} elements. | If {{tt|n}} is greater than the number of elements in the sequence, selects {{c|last-first}} elements. | ||
| − | The algorithm is stable only if {{tt|PopulationIterator}} meets the requirements of {{named req|ForwardIterator}} | + | The algorithm is stable (preserving the relative order of the selected elements) only if {{tt|PopulationIterator}} meets the requirements of {{named req|ForwardIterator}} |
===Parameters=== | ===Parameters=== | ||
Revision as of 11:53, 5 November 2018
| Defined in header <algorithm>
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| template< class PopulationIterator, class SampleIterator, class Distance, class URBG > |
(since C++17) | |
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. Random numbers are generated using the random number generator g.
If n is greater than the number of elements in the sequence, selects last-first elements.
The algorithm is stable (preserving the relative order of the selected elements) only if PopulationIterator meets the requirements of LegacyForwardIterator
Contents |
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.
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-SampleIterator must meet the requirements of LegacyOutputIterator.
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-SampleIterator must also meet the requirements of LegacyRandomAccessIterator if PopulationIterator doesn't meet LegacyForwardIterator
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-PopulationIterator's value type must be writeable to out
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-Distance must be an integer type
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-std::remove_reference_t<URBG> must meet the requirements of UniformRandomBitGenerator and its return type must be convertible to Distance
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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 <algorithm> int main() { std::string in = "abcdefgh", out; std::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 : adfgh
See also
| (until C++17)(C++11) |
randomly re-orders elements in a range (function template) |
