Vectors and printing to a file

[apmca]

How might I go about doing the following in C++?:

Define vectors "v" and "w" (doesn't really matter what they are) and then redefine "v" as the concatenation of "v" and "w".

For example, if I have v = [1,2,3] and w = [4,5,6], I want to redefine v = [v,w] = [1,2,3,4,5,6].

[apmca]

Also, how would I print the result "v" to a text file?

[Paul McKenzie]

How might I go about doing the following in C++?:

The term "vector" has a special meaning in C++. Are you talking about the container std::vector<T>, or something else?

Regards,

Paul McKenzie

[apmca]

Sorry, I'm new to C++

I just need something that will act like a (mathematical) vector (say, the C++ analogue of a vector in MATLAB or Mathematica).

[Amleto]

http://www.cplusplus.com/reference/stl/vector/insert/

if you want to print to file you might find fstream useful.

[Lindley]

For the above task, std::vector::insert() is sufficient as stated.

However, for anything more mathematical, you should consider using Boost::uBLAS's vector class.

[Speedo]

Are you talking about a mathematical vector as in this? Or a vector as some container holding objects?

I ask because while you said you're talking about a math vector, your concatenation example in the OP looks more like you want a container...

[Paul McKenzie]

How might I go about doing the following in C++?:

Define vectors "v" and "w" (doesn't really matter what they are) and then redefine "v" as the concatenation of "v" and "w".

For example, if I have v = [1,2,3] and w = [4,5,6], I want to redefine v = [v,w] = [1,2,3,4,5,6].

What if v = [1,2,3] and w = [3,4]? Would combining the two vectors be [1,2,3,4]?

If so, then use a container such as std::vector and then the std::set_union() algorithm function to combine the elements using "union" as the set operation.

Here is a small example using a vector of strings. Change this to the data type you want to use (in your case, probably int).

#include <vector>
#include <algorithm>
#include <string>
#include <iterator>

int main()
{
   std::vector<string> v(3);
   std::vector<string> w(2);
   std::vector<string> result;

   v[0] = "Joe"; 
   v[1] = "John";
   v[2] = "Susan";

   w[0] = "Susan";
   w[1] = "Jack";

   std::set_union(v.begin(), v.end(), w.begin(), w.end(), std::back_inserter(result));
    
   // now result is a vector that has ["Joe", "John", "Susan", "Jack"] as elements.  
v = result; // set v equal to the result
}

Regards,

Paul McKenzie

[apmca]

What if v = [1,2,3] and w = [3,4]? Would combining the two vectors be [1,2,3,4]?

If so, then use a container such as std::vector and then the std::set_union() algorithm function to combine the elements using "union" as the set operation.

Here is a small example using a vector of strings. Change this to the data type you want to use (in your case, probably int).

#include <vector>
#include <algorithm>
#include <string>
#include <iterator>

int main()
{
   std::vector<string> v(3);
   std::vector<string> w(2);
   std::vector<string> result;

   v[0] = "Joe"; 
   v[1] = "John";
   v[2] = "Susan";

   w[0] = "Susan";
   w[1] = "Jack";

   std::set_union(v.begin(), v.end(), w.begin(), w.end(), std::back_inserter(result));
    
   // now result is a vector that has ["Joe", "John", "Susan", "Jack"] as elements.  
v = result; // set v equal to the result
}

Regards,

Paul McKenzie

Thanks for the reply. In the case that v = [1,2,3] and w = [3,4], I would actually be looking for v = [1,2,3,3,4] instead of just the union.

Additionally, when I type cout << v at the end I am getting an error. How do you display the vector that's saved?

[Amleto]

iterate over all the elements of the vector, and output the de-referenced iterator.

pseudo:

std::vector<int> vec;
// fill up the vector...

std::vector<int>::iterator iter;
loop

  cout << *iter;

end loop