Sorting an array of structs by particular members of said structs?

Question

So basically, I have a struct that, along with other members, has x, y and z values to represent a 3D point; I have then a vector of said structs which is built by some functions.

struct myStruct{
    char x;
    char y;
    char z;
    // some other members
};

vector<myStruct> myVector = myVectorBuildingFunction(...);

Now, I would like to sort the structs in the vector by the distance between their 3D point (x, y, z members) and another variable point in the space.. is that possible without rebuilding the structs' members one by one (they're relatively many) or remaking entirely my initial vector building function?

Why the DirectX tag? This is a question about sorting a struct - the fact that you might be using it in DX is not relevant to the question. — Roger Rowland, Jul 14 '13 at 08:50

score 2 · Accepted Answer · answered Jul 13 '13 at 23:35

2

You can use std::sort with lambdas, like this:

myStruct pointOfInterest = ...; // Set the point of interest
sort(mMyClassVector.begin(), mMyClassVector.end(), 
    [&](const myStruct & lhs, const myStruct & rhs) -> bool
{
    double distanceLhs = computeDistance(pointOfInterest, lhs);
    double distanceRhs = computeDistance(pointOfInterest, rhs);
    return distanceLhs < distanceRhs;
});

answered Jul 13 '13 at 23:35

Sergey Kalinichenko

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Or can overload the `operator()` in the structure, if this is what you will be taking as a comparision metric for complete course of your program. Just a suggestion. – Aman Deep Gautam Jul 13 '13 at 23:38
1

@AmanDeepGautam That would be harder, because you would need to store the point of interest inside the comparator structure. Lambdas provide a more concise approach to this problem. – Sergey Kalinichenko Jul 13 '13 at 23:41
@dasblinkenlight I am kind of confused here with the statement "distance between their 3D point" in the question. I think everything is in the structure itself is what OP meant. I may be wrong. I know it is intuitive to find distance from some other point(like origin) but I am not sure if it is that metric here. – Aman Deep Gautam Jul 13 '13 at 23:48
@AmanDeepGautam My understanding is that `myStruct` has other members in addition to `x`, `y`, and `z`. The first three members represent "their point", the rest of the members are not used for comparison. – Sergey Kalinichenko Jul 13 '13 at 23:50
@dasblinkenlight Yup, that's exactly what I meant. Er pardon me, is computeDistance() a function I have to write or is it an actual function..? – Banderi Jul 13 '13 at 23:55
@Banderi Yes, that's a function that you need to write. This could be a member function on the `myStruct` as well, and it does not have to take `myStruct` as a second parameter - a 3D point would work as well. – Sergey Kalinichenko Jul 13 '13 at 23:57
@dasblinkenlight apparently what you understood was correct. I think sometimes we should just go by intuition..:) – Aman Deep Gautam Jul 14 '13 at 00:09

score 1 · Answer 2 · edited May 23 '17 at 12:29

1

Yes, it's possible using comparator function or functors.

struct byDistTo {
   myStruct point;
   byDistTo(myStruct point): point(point){}
   bool operator() (const& myStruct a, const& myStruct b) const {
     // define getDistance yourself
     return getDistance(a, point) < getDistance(b, point); 
   }
}

And later call std::sort:

vector<myStruct> myVector = myVectorBuildingFunction(...);
myStruct point = {1,2,3}; // define that 'another varialbe`
std::sort(myVector.begin(), myVector.end(), byDistTo(point));

edited May 23 '17 at 12:29

Community

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answered Jul 13 '13 at 23:37

sasha.sochka

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It is better to define `by_dist` in the scope of `myStruct`. isn't it? – Aman Deep Gautam Jul 13 '13 at 23:39

Sorting an array of structs by particular members of said structs?

2 Answers2