How to copy a vector except one specific element? - c++

Question

I have a vector with some values. How can I copy it to another vector, so all the values but a specific one (located at position x - x will be a parameter of course) would be copied?
Moreover, I would like to use the value from location x for something else, so I prefer it will be saved.
Is there an easy way to do it?

Answer 1

How to copy stl vector except one specific value?
You can use std::copy_if:
std::vector<T> v = ....;
std::vector<T> out;
T x = someValue;
std::copy_if(v.begin(), v.end(), std::back_inserter(out),
[x](const T& t) { return t != x; });
If you don't have C++11 support, you can use std::remove_copy_if and adjust the predicate's logic accordingly.

Answer 2

use std::copy_if if you have c++11, otherwise:
void foo(int n) {
std::vector<int> in;
std::vector<int> out;
std::copy(in.begin(), in.begin() + n, out.end());
std::copy(in.begin() + n + 1, in.end(), out.end());
}
This works because std::vector has random-access iterators.

Answer 3

As Luchian suggests, you should use erase()
#include <vector>
#include <iostream>
#include<algorithm>
int main(){
std::vector<int> vec1;
vec1.push_back(3);
vec1.push_back(4); // X in your question
vec1.push_back(5);
std::vector<int> new_vec;
new_vec = vec1;
new_vec.erase(std::find(new_vec.begin(),new_vec.end(),4));
for (unsigned int i(0); i < new_vec.size(); ++i)
std::cout << new_vec[i] << std::endl;
return 0;
}
and for your second question, to determine the index of an element in a vector
// determine the index of 4 ( in your case X)
std::vector<int>::iterator it;
it = find(vec1.begin(), vec1.end(), 4);
std::cout << "position of 4: " << distance(vec1.begin(),it) << std::endl;