I have an std::vector of pairs of defined as the following structure:
template<typename Iterator>
struct Pair{
double a;
Iterator iterator;
};
Asked
Active
Viewed 164 times
0
1 Answers
2
You can give a custom comparator to sort, as a lambda:
std::sort(vec.begin(), vec.end(), [](const auto& lhs, const auto& rhs) {return lhs.a < rhs.a;});
Note: the above is C++14 syntax. If you wish it to be compliant with C++11, you simply change the const auto& in the above to the const & actual type of the vector, e.g. const Pair<MyIter>&.
Smeeheey
- 9,906
- 23
- 39
-
You need to mention that this is C++17 – Slava Jun 09 '16 at 13:57
-
1It isn't, its C++14. In any case, its trivial to edit above to be C++11, this was more for brevity – Smeeheey Jun 09 '16 at 13:57
-
Yes my mistake, but it should be mentioned anyway – Slava Jun 09 '16 at 13:58
-
OK, fair enough. I will edit – Smeeheey Jun 09 '16 at 13:58
-
1@Slava Why? The Q is tagged C++ and that covers up to the current standard. – NathanOliver Jun 09 '16 at 13:59
-
I have now edited my OP with the code I want to work with your implementations but it still gives me a long error when I try to compile. Did I implement it wrong? – Andreas Mortensen Jun 09 '16 at 14:10
-
`std::sort` does not return anything, it sorts the given vector in-place. Get rid of the `distPairs =` bit on your `sort` line – Smeeheey Jun 09 '16 at 14:16
-
it seems I still get a long error from the compiler even after removing distPairs – Andreas Mortensen Jun 09 '16 at 14:36
-
The body of your comparator lambda is also wrong - it needs to be `{return lhs.a < rhs.a;}` – Smeeheey Jun 09 '16 at 14:40
-
but in the sample code I uploaded my array of pairs is called distance_pairs – Andreas Mortensen Jun 09 '16 at 15:11
-
The code you actually need is `{return lhs.distance < rhs.distance;}` (I just saw that in your real type the member is called `distance` not `a`). Why? The lambda is not comparing the *arrays* but rather their *members*. – Smeeheey Jun 09 '16 at 15:15
-
If I now want to extract an array of the first n iterators in the sorted list of pairs. How can I then do this easily? I.e. I want to extract this from my sorted list of pairs distance_pairs. – Andreas Mortensen Jun 09 '16 at 16:54
-
No. Something more like (after dist_pair is created) `std::vector
a; std::generate_n(std::back_inserter(a), k, [it = dist_pair.begin()](){ return (it++)->iterator;}); return a;` – Smeeheey Jun 09 '16 at 22:16