adding elements of a vector to an unordered set

Question

Is there an easy way to add all the elements of a vector to an unordered_set? They are of the same type. Right now, I am using a for loop and was wondering if there is a better way to do it

score 63 · Accepted Answer · answered Oct 12 '12 at 01:28

63

If you're constructing the unordered_set then:

std::vector<int> v;
std::unordered_set<int> s(v.begin(), v.end());

answered Oct 12 '12 at 01:28

mythagel

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what should be done next? I've tried this, but it doesn't seem to build the set. E.g. ```vector v; set s(v.begin(), v.end()); for(...) // here I push back elements for( auto i : s) cout << i;``` doesn't print anything, and debugging shows the set is empty. – 101is5 Sep 18 '22 at 12:33

score 27 · Answer 2 · answered Oct 12 '12 at 01:21

27

Forgive me if my syntax has any minor bugs, but you can try the std::copy function, its meant for this purpose.

std::vector<int> v;
std::unordered_set<int> s;
std::copy(v.begin(),v.end(),std::inserter(s,s.end()));

answered Oct 12 '12 at 01:21

Karthik T

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`std::inserter` is required to insert into an associative container. – James McNellis Oct 12 '12 at 01:22
yup, i knew i missed something, fixed. – Karthik T Oct 12 '12 at 01:26
2

does s.end() remain valid even if the container rehashes? – Johannes Schaub - litb Dec 09 '14 at 13:39
if v is empty then an 0 will be added to s! – James Harper Jul 08 '15 at 17:19

adding elements of a vector to an unordered set

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