[C++] Sorting a Vector of vectors

[Andre S. Veteran]

Hello,

I have an entity in 3D, which is defined by a std::vector of points. Each point is an std::vector containing three values :, X, Y and Z.

So it's really a vector< vector< int > >.

I want to find the geometrical center of the 3D entity. To do this, I think I have to find the minimum X and maximum X, and take the value in-between, repeat for Y, repeat for Z; those three values are the center.

I could of course proceed with a bunch of for loops but this is tedious. To find maximum and minimum values, I could more easily use the sort algorithm of the STL. I'm a bit clueless at how I would implement this, though. Yes generally speaking I know how to implement a functor for an algorithm but in this case my brain refuses to cooperate.

Any help is appreciated.

[rpgfan]

If I read your post right, your vector of vectors is structured like this:

VectorList< Vector<int>[3] = {x, y, z} > (an arbitrarily-sized list of vectors, where each vector contains 3 elements)

and you want to find the geometrical center. There isn't anything in the STL that can do it this way because of your structure. Honestly, you've got the organization a bit backward for the goal you're trying to achieve. It would be a lot simpler if the inner vector was a list of (x/y/z)-coordinates, and the outer vector contained each inner vector, something like this:

VectorList< Vector<int> >[3] (a list of 3 vectors, where each vector is of arbitrary size)

You might create a function that returns a vector as described with the input being your own implementation, and then pass the result as an argument to the actual function that computes the geometric center, which might make use of things from the <algorithm> header like std::min_element() and std::max_element(). FWIW, I said a conversion function would be useful because both have their strengths and weaknesses.

I've got the code ready, but it seems like you really enjoy programming; I think I'll let you think about it. ^_^

I hope this helps!

[gigapixels Veteran]

I'm not sure why you are using a vector to store a static number of variables.

In my opinion, a better way would be to create a Point class and a PointVector class (or however you want to name them). The Point class would simply hold the x, y, and z coordinates and have methods to access and edit those values, and the PointVector class would implement a vector to hold those points. You could then create methods in the PointVector class to sort by whichever point you want or give you min and max of whichever point. Such simple classes wouldn't take very long to write.

[Andre S. Veteran]

I am in no way responsible for the poor design, this is an assignment. I cannot change the provided implementation AFAIK, I have to work with it.

So it seems my brain refused to cooperate because there's no evident way of doing it with STL algorithms. Sigh. I guess I'll do what rpgfan suggested.

Thanks. :)

[gigapixels Veteran]

Ah, alright. Nevermind my suggestion then ;)

And yes, given the organization of the data, you cannot use any automated STL method. For loops it is! :laugh: