Combining vectors of string's

Question

I have a number of vectors of strings each containing dates. As a simple example vector A of size 2 might contain:

A[0] = "01-Jul-2010"; 
A[1] = "03-Jul-2010";

while a second vector B of size 3 might contain:

B[0] = "02-Jul-2010";
B[1] = "03-Jul-2010"; 
B[2] = "04-Jul-2010";  

I'd like to form a vector C which contains the 'union' of the element in A and B:

C[0] = "01-Jul-2010";
C[1] = "02-Jul-2010";
C[2] = "03-Jul-2010";
C[3] = "04-Jul-2010"; 

When combining A and B I don't want any repeated dates so each element of C must be unique. Is there any in-built/stl (or Boost library) function I can call that will do this?

Thanks!

Answer 1

There is a set_union function in STL to find the union of two (lexicographically) sorted sequences. Assuming A and B are already sorted,

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

...

std::vector<std::string> C;
std::set_union(A.begin(), A.end(), B.begin(), B.end(), std::back_inserter(C));

---

If A and B are sorted by date, you need to supply that date-comparing function / functor, e.g.

bool is_earlier(const std::string& first_date, const std::string& second_date) {
   // return whether first_date is earlier than second_date.
}

...

std::set_union(A.begin(), A.end(), B.begin(), B.end(),
               std::back_inserter(C), is_earlier);