How to manipulate vectors in C++

Question

I'm trying to manipulate a set of elements in vectors in c++.

vector <int> vectorOfValue;

vectorOfValue.push_back(1);
vectorOfValue.push_back(2);
vectorOfValue.push_back(3);
vectorOfValue.push_back(4);
vectorOfValue.push_back(5);
vectorOfValue.push_back(6);
vectorOfValue.push_back(7);
vectorOfValue.push_back(8);
vectorOfValue.push_back(9);
vectorOfValue.push_back(10);

I would like to know how the program can print out the vectors of values bigger 3 and smaller than 9.

It is a set of the data to exclude the outliers for example.

What you would like to do is very simple, Being able to do just that with help from other SO users is not going to help you in the long run. Please pick up [a good book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) and learn the basics of the language. — R Sahu, Dec 18 '17 at 17:17

score 4 · Answer 1 · answered Dec 18 '17 at 17:19

4

If you want to use the standard library algorithms and iterators, you could use std::copy_if:

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>

auto main(int argc, char* argv[]) -> int
{
  std::vector<int> vectorOfValue;
  // code for initialization of vector ..

  std::copy_if(vectorOfValue.begin(), 
               vectorOfValue.end(), 
               std::ostream_iterator<int>(std::cout, "\n"), 
               [](const int value) { return value > 3 && value < 9; });
}

answered Dec 18 '17 at 17:19

Christian G

943
9
16

Since the OP says *program can print out the vectors*. A simple iteration would have done. `for (vector::iterator it = vec.begin() ; it != vec.end(); ++it)if(*it>3 && *it<9)cout << *it << ' ';` Any specific reasons for `copy_if` ? Genuinely curious! – Aditi Rawat Dec 18 '17 at 17:27
@AditiRawat why not a range-for-loop? `for (auto value : vectorOfValue) if (value > 3 && value < 9) cout << value << ' ';` – mch Dec 18 '17 at 17:28
Lately I am minimizing my use of for-loops if there is an appropriate std algorithm, generally prefering the "collections-way" of doing things. You might be interested in this article: https://advancedweb.hu/2017/11/21/a_detailed_case_study_against_for/ – Christian G Dec 18 '17 at 17:30

score -1 · Accepted Answer · answered Dec 19 '17 at 04:56

-1

Short approach of mine using auto syntax instead of using iterator :

for(auto &i : vectorOfValue) {
   if (i > 3 && i < 9) {
      std::cout << i << std::endl;
   }
}

answered Dec 19 '17 at 04:56

Tirtadwipa Manunggal

117
1
4

How do calculate the mean for that set of numbers in this case std::cout << i << std::endl;? – VictorMF Dec 19 '17 at 21:08
sum the `i` and store it in a variable, then divide it by the size of data – Tirtadwipa Manunggal Dec 20 '17 at 01:38
you shouldn't use std::endl here and you should not take i per reference – Christian G Jul 16 '18 at 14:27

How to manipulate vectors in C++

2 Answers2