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I guess this is a simple question. I need to do something like this:
std::set<int> s1, s2; s1 = getAnExcitingSet(); std::transform(s1.begin(), s1.end(), std::back_inserter(s2), ExcitingUnaryFunctor()); Of course, std::back_inserter doesn't work since there's no push_back. std::inserter also needs an iterator? I haven't used std::inserter so I'm not sure what to do.
Does anyone have an idea?
s2, and then just sort it later. Maybe that's better?
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std::back_inserter A back-insert iterator is a special type of output iterator designed to allow algorithms that usually overwrite elements (such as copy ) to instead insert new elements automatically at the end of the container.
std::inserter constructs an insert iterator that inserts new elements into x in successive locations starting at the position pointed by it. It is defined inside the header file .
std::transform on a range For example, to obtain the keys that a map contains, you can use std::transform the following way: map<int, string> m = { {1,"foo"}, {42, "bar"}, {7, "baz"} }; vector<int> keys; std::transform(m. begin(), m. end(), std::back_inserter(keys), getFirst);
std::equal_range on bidirectional iterators is extremely slow, because it has to walk step by step through the range. The std::set. find method, on the other hand, uses the tree structure of std::set to find the element really fast. It can, basically, get midpoints of a range really fast.
set doesn't have push_back because the position of an element is determined by the comparator of the set. Use std::inserter and pass it .begin():
std::set<int> s1, s2; s1 = getAnExcitingSet(); transform(s1.begin(), s1.end(), std::inserter(s2, s2.begin()), ExcitingUnaryFunctor()); The insert iterator will then call s2.insert(s2.begin(), x) where x is the value passed to the iterator when written to it. The set uses the iterator as a hint where to insert. You could as-well use s2.end().
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