vo004_SortAndSelect.C File Reference

Detailed Description

In this tutorial we learn how elements of an RVec can be easily sorted and selected.

 
void vo004_SortAndSelect()
{
   // Because RVec implements an iterator, the class is fully compatible with
   // the sorting algorithms in the standard library.
   ROOT::RVecD v1{6., 4., 5.};
   ROOT::RVecD v2(v1);
   std::sort(v2.begin(), v2.end());
   std::cout << "Sort vector " << v1 << ": " << v2 << std::endl;
 
   // For convenience, ROOT implements helpers, e.g., to get a sorted copy of
   // an RVec ...
   auto v3 = Sort(v1);
   std::cout << "Sort vector " << v1 << ": " << v3 << std::endl;
 
   // ... or a reversed copy of an RVec.
   auto v4 = Reverse(v1);
   std::cout << "Reverse vector " << v1 << ": " << v4 << std::endl;
 
   // Helpers are provided to get the indices that sort the vector and to
   // select these indices from an RVec.
   auto i = Argsort(v1);
   std::cout << "Indices that sort the vector " << v1 << ": " << i << std::endl;
 
   ROOT::RVecD v5{9., 7., 8.};
   auto v6 = Take(v5, i);
   std::cout << "Sort vector " << v5 << " respective to the previously"
             << " determined indices: " << v6 << std::endl;
 
   // Take can also be used to get the first or last elements of an RVec.
   auto v7 = Take(v1, 2);
   auto v8 = Take(v1, -2);
   std::cout << "Take the two first and last elements of vector " << v1
             << ": " << v7 << ", " << v8 << std::endl;
 
   // Because the helpers return a copy of the input, you can chain the operations
   // conveniently.
   auto v9 = Reverse(Take(Sort(v1), -2));
   std::cout << "Sort the vector " << v1 << ", take the two last elements and "
             << "reverse the selection: " << v9 << std::endl;
}

 
Sort vector { 6, 4, 5 }: { 4, 5, 6 }
Sort vector { 6, 4, 5 }: { 4, 5, 6 }
Reverse vector { 6, 4, 5 }: { 5, 4, 6 }
Indices that sort the vector { 6, 4, 5 }: { 1, 2, 0 }
Sort vector { 9, 7, 8 } respective to the previously determined indices: { 7, 8, 9 }
Take the two first and last elements of vector { 6, 4, 5 }: { 6, 4 }, { 4, 5 }
Sort the vector { 6, 4, 5 }, take the two last elements and reverse the selection: { 6, 5 }

Date

August 2018

Author

Stefan Wunsch

Definition in file vo004_SortAndSelect.C.