CODEWITHSUNDEEP
c++vector
Kara
Kara

Reputation: 785

subtract values from elements in a vector C++

I have two vectors with the values

2.123, 2.111, 9.222
1.22, 4.33, 2.113

I want to subtract the first element of each Vector with each other, the second element of each Vector, and the third. so

abs(2.123-1.22)
abs(2.111-4.33)
abs(9.222-2.113)

I'm pretty sure you have to create a for loop but I'm not sure how to approach this problem as I am new to C++. Thank you all for your help.

The code below is a general concept of what I have

std::vector<double> data1, vector<double> data2, vector<double> result;
std::cout << "Enter in data#1 ";
std::cin >> data1;

std::cout << "Enter in data#2 ";
std::cin >> data2;

for (int i=0;i<data1.size();i++){
    //start subtracting the values from each other and have them stored in another Vector

Upvotes: 10

Views: 14719

Answers (3)

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

If you do not know yet standard algorithms as suggested here algorithm std::transform you can write an equivalent code using an ordinary for statement. For example

std::vector<double> a { 2.123, 2.111, 9.222 };
std::vector<double> b { 1.22, 4.33, 2.133 }; 
std::vector<double> c( a.size(), 0.0 );


for ( std::vector<double>::size_type i = 0; i < a.size(); i++ )
{
   c[i] = std::abs( a[i] - b[i] );
}

Upvotes: -4

Jerry Coffin
Jerry Coffin

Reputation: 490108

You'd probably (at least normally) want to do this with std::transform:

std::vector<double> a{2.123, 2.111, 9.222}, 
                    b{1.22, 4.33, 2.133}, 
                    c;

std::transform(a.begin(), a.end(), b.begin(), std::back_inserter(c),
    [](double a, double b) { return fabs(a-b); });

Upvotes: 12

Zac Howland
Zac Howland

Reputation: 15872

Assuming they are both the same size:

std::vector<double> a;
std::vector<double> b;
// fill in a and b
std::vector<double> result;
std::transform(a.begin(), a.end(), b.begin(), std::back_inserter(result), [&](double l, double r)
{
    return std::abs(l - r);
});

Upvotes: 13

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