I have two boost intrusive sets which I need to merge it together. I have map_old.m_old_attributes
boost intrusive set which I need to merge it to m_map_new_attributes
boost intrusive set
void DataTest::merge_set(DataMap& map_old)
{
// merge map_old.m_old_attributes set into m_map_new_attributes
}
What is the best way to do this? I am not able to find a function which can do the merge for me? I recently started working with boost intrusive sets and I am not able to find predefined methods which can do the merge, or may be I am wrong?
Indeed intrusive sets are a different beast. They don't manage their element allocations.
So when merging you need to decide what that means. I'd say a reasonable interpretation would be that you want to move the elements contained inside the map_old
container into the DataMap.
This would leave map_old
empty. Here's such an algorithm:
template <typename Set>
void merge_into(Set& s, Set& into) {
std::vector<std::reference_wrapper<Element> > tmp(s.begin(), s.end());
s.clear(); // important! unlinks the existing hooks
into.insert(tmp.begin(), tmp.end());
}
Update Alternately you can do it with O(1) memory complexity by using the slightly trickier iterater-erase-loop (beware of iterating mutating containers): Live On Coliru as well
for (auto it = s.begin(); it != s.end();) { auto& e = *it; it = s.erase(it); into.insert(e); }
See it Live On Coliru
#include <boost/intrusive/set.hpp>
#include <boost/intrusive/set_hook.hpp>
#include <string>
#include <vector>
#include <functional>
#include <iostream>
namespace bive = boost::intrusive;
struct Element : bive::set_base_hook<> {
std::string data;
Element(std::string const& data = "") : data(data) {}
bool operator< (Element const& rhs) const { return data < rhs.data; }
bool operator==(Element const& rhs) const { return data ==rhs.data; }
};
using Set = bive::set<Element>;
template <typename Set>
void merge_into(Set& s, Set& into) {
std::vector<std::reference_wrapper<Element> > tmp(s.begin(), s.end());
s.clear(); // important! unlinks the existing hooks
into.insert(tmp.begin(), tmp.end());
}
int main() {
std::vector<Element> va {{"one"},{"two"},{"three"},{"four"},{"five"},{"six"},{"seven"},{"eight"},{"nine"} };
Set a;
for(auto& v : va) a.insert(v);
std::vector<Element> vb {{"two"},{"four"},{"six"},{"eight"},{"ten"} };
Set b;
for(auto& v : vb) b.insert(v);
assert(9==a.size());
assert(5==b.size());
merge_into(a, b);
assert(a.empty());
assert(10==b.size());
}
Of course you can come up with different semantics for the merge operation (which would be more akin to 'copy' instead of 'move')