Sort vector of 3D point by X axis

[Abdullah30]

I have a difficulty. I want to sort a vector <PointType> myVector by X axis increasing or decreasing, whatever. PointType is a type defined in ITK and typedef itk::Point<double,3> PointType;

- Can't we use the function sort of std vector to sort a vector in 3 dimensions based on a component?

- It would be the quickest way to sort this vector points according to the X axis.

- I tried to bubble sort but that didn't helped. I am still a novice in C++ so I probably take me wrong level data structures.

The result does not seem correct to me either?

void Exchange(vector<PointType> table, const int i, const int j)
{
int temp1,temp2,temp3;
temp1 = table[i][0];
temp2 = table[i][1];
temp3 = table[i][2];

table[i][0] = table[j][0];
table[i][1] = table[j][1];
table[i][2] = table[j][2];

table[j][0] = temp1;
table[j][1] = temp2;
table[j][2] = temp3;
}

void triABubble(vector<PointType> table,int length)
{
bool permutation;
do
{
permutation = false;
for(int i=0; i<length-1; i++)
{
if(table[i][0]>table[i+1][0])
{
Exchange(table, i, i+1);
permutation = true;
}
}
length--;
}
while(permutation);
}

[CitricAcid]

To sort your vector you can use this:

std::sort(vector.begin(), vector.end(), myCompareLess);
with the defined function :
bool myCompareLess(PointType *p1, PointType *p2)
{
  // returns true if p1 <p2 based on criteria that you want
}

[absolute55]

Can't we use the function sort of std vector to sort a vector in 3 dimensions based on a component?

Yes, passing a function performing the test on component that interests you.

For CitricAcid suggestion, it works unless you take references instead of pointers

Why not just implement the "<" operator in class PointType?

[kelfro]

Why to use operator < because it would just test only the X axis?

<time prog. generic>
the plan would be good to have a class of predicate template type:

template<int Idx> struct order_by_component;
template<> struct order_by_component<1>
{
   bool operator ()( PointType const& i,PointType const& j) { return /* test on x */; }
};
template<> struct order_by_component<2>
{
   bool operator ()( PointType const& i,PointType const& j) { return /* test on y */; }
};
template<> struct order_by_component<3>
{
   bool operator ()( PointType const& i,PointType const& j) { return /* test on z */; }
};

</ time prog. generic>

[Abdullah30]

Thank you for all your responses. As I mentioned, I am new to c++. So I tested one of the proposed solution with the lot but I do not know how to retrieve evidence;

bool myCompareLess(PointType pt1, PointType pt2)
{
if (pt1[0]<pt2[0])
return true;
else
return false;
}

sort(vect.begin(), vect.end()-1, myCompareLess(vect[vect.begin()],vect[vect.begin()+1]);

I tested this but in vain