Re: erase vector v2 elements from v1
Obnoxious User wrote:
On Sun, 04 Jan 2009 09:57:32 -0800, James Juno wrote:
Hi folks,
Rudimentary container question. I have something like
std::vector<int> v1;
std::vector<int> v2;
I want to remove all elements in v2 from v1. Right now I'm using this
horrible non-STL loop:
for ( size_t i = 0; i < v1.size(); ++i ) for ( size_t j = 0; j <
v2.size(); ++j ) {
if ( v1[i] == v2[j] )
{
v1.erase( v1.begin() + i );
break;
}
}
Yuck. There has got to be a cleaner, more STL-like way of doing this.
Moreover, it may incur undefined behavior since the loop can easily read
beyond the end of v1.
#include <iterator>
#include <algorithm>
template<typename Container>
void exclude(Container & values, Container & remove, Container & output) {
/*
If 'values' and 'remove' already are sorted, then
these two calls can be removed and you can add 'const'
in the parameter list. Or create sorted temporaries.
*/
std::sort(values.begin(),values.end());
std::sort(remove.begin(),remove.end());
std::set_difference(values.begin(),values.end(),
remove.begin(),remove.end(),std::back_inserter(output));
}
Just a note: if output is the same vector as values or remove, funny results
are certain. One might want to document that in the contract of exclude().
Best
Kai-Uwe Bux