How to get the minimum or maximum element in a vector of structures in C++, based on some field in the structure

Question

How can I get the minimum or maximum element in a vector of structures in C++, based on some field in the structure?

For example:

struct Size {
    int width, height;
};
vector<Size> sizes;

And now I want to solve that based on width and create a new vector for that. And then sort based on height and create a new vector for that.

Answer 1

In C++11, you can use the std::minmax_element() standard function, which (given a pair of iterators) and possibly a custom comparator (that would allow you to define the field on which the ordering is based), will return you an iterator to the minimum and an iterator to the maximum element, packed in an std::pair.

So for instance:

#include <algorithm> // For std::minmax_element #include <tuple> // For std::tie #include <vector> // For std::vector #include <iterator> // For global begin() and end()  std::vector<Size> sizes = { {4, 1}, {2, 3}, {1, 2} };  decltype(sizes)::iterator minEl, maxEl; std::tie(minEl, maxEl) = std::minmax_element(begin(sizes), end(sizes),     [] (Size const& s1, Size const& s2)     {         return s1.width < s2.width;     }); 

Here is a live example.

Answer 2

You can use std::min_element and std::max_element with a suitable functor:

bool cmp(const Size& lhs, const Size& rhs) {   return lhs.width < rhs.width; } 

then

auto min_it = std::min_element(sizes.begin(), sizes.end(), cmp); auto max_it = std::max_element(sizes.begin(), sizes.end(), cmp); 

In C++11 you can replace cmp with a lambda expression.

See also: std::minmax_element

Answer 3

vector<Size> sizes;
...
vector<Size> sortedByWidths(sizes);
vector<Size> sortedByHeights(sizes);
sort(sortedByWidths.begin(), sortedByWidths.end(), 
    [](Size s1, Size s2) {return s1.width < s2.width;});
sort(sortedByHeights.begin(), sortedByHeights.end(), 
    [](Size s1, Size s2) {return s1.height< s2.height;});