algorithm to add values of two ranges and place th

问题:

I was just wondering if there was anything (either in c++11 or boost) that could help me do something like this:

std::vector<int> v1 = {1, 2, 3};
std::vector<int> v2 = {2, 5, 4};
std::list<int> res;
algorithm(v1.begin(), v1.end(), v2.begin(), v2.end(), back_inserter(res), std::plus<int>());

the result should of course be {3, 7, 7} and where instead of std::plus could be any binary_function.

So if anyone has an idea, let me know.

回答1:

You can use the 5 parameter overload of std::transform for this. This takes a binary functor to operate on pairs of elements of two ranges:

std::transform(v1.begin(), 
               v1.end(), 
               v2.begin(), 
               back_inserter(res), 
               std::plus<int>());

回答2:

Just for fun, I'll point to an alternative to std::vector and std::transform. You could use std::valarray instead.

#include <valarray>
#include <iostream>

int main() { 
    std::valarray<int> a = {1, 2, 3};
    std::valarray<int> b = {2, 5, 4};

    std::valarray<int> c = a + b;    // look ma, no transform!

    for (int i=0; i<3; i++)
        std::cout << c[i] << "\t";
}

Result:

3       7       7

Unfortunately, even though the code for adding the valarrays together is simple and clean, valarray has never gained much popularity. As such, we're left with this rather strange situation where even code like that above that strikes me as very clean, straightforward and readable still almost qualifies as obfuscated, simply because so few people are accustomed to it.

回答3:

std::transform is what you are looking for.

回答4:

std::transform (http://en.cppreference.com/w/cpp/algorithm/transform) is what you might be looking for.