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(C++) MakeAbs

 

Math code snippet to make all elements in a container positive.

 

There are multiple ways to implement MakeAbs:

  1. Using an algorithm (preferred [1][2])
  2. Using a for-loop

 

 

 

 

 

MakeAbs using an algorithm

 

#include <algorithm>
#include <cmath>
#include <functional>
#include <vector>

template <class T> struct Abs : public std::unary_function<T,T>
{
  const T operator()(const T& x) const { return std::abs(x); }
};

void MakeAbs(std::vector<int>& v)
{
  std::transform(v.begin(),v.end(),v.begin(),Abs<int>());
}

 

Note: I did not find any way to refrain from writing a functor (for example, by using std::ptr_fun) as shown in the lines below...

 

std::transform(v.begin(),v.end(),v.begin(),std::abs); //Does not work
std::transform(v.begin(),v.end(),v.begin(),&std::abs); //Does not work
std::transform(v.begin(),v.end(),v.begin(),std::ptr_fun(&std::abs)); //Does not work
std::transform(v.begin(),v.end(),v.begin(),std::ptr_fun(std::abs)); //Does not work

 

 

 

 

 

MakeAbs using a for-loop

 

#include <cmath>
#include <vector>
 
void MakeAbs(std::vector<int>& v)
{
  const int sz = v.size();
  for (int i=0; i!=sz; ++i)
  {
    v[i] = std::abs(v[i]);
  }
}

 

 

 

 

 

References

 

  1. Bjarne Stroustrup. The C++ Programming Language (3rd edition). ISBN: 0-201-88954-4. Chapter 18.12.1 : 'Prefer algorithms over loops'
  2. Herb Sutter and Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. ISBN: 0-32-111358-6. Chapter 84: 'Prefer algorithm calls to handwritten loops.'

 

 

 

 

 

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