I have a vector of objects and want to delete by value. However the value only occurs once if at all, and I don't care about sorting.
Obviously, if such delete-by-values were extremely common, and/or the data set quite big, a vector wouldn't be the best data structure. But let's say I've determined that not to be the case.
To be clear, if my code were C, I'd be happy with the following:
void delete_by_value( int* const piArray, int& n, int iValue ) {
for ( int i = 0; i < n; i++ ) {
if ( piArray[ i ] == iValue ) {
piArray[ i ] = piArray[ --n ];
return;
}
}
}
It seems that the "modern idiom" approach using std::algos and container methods would be:
v.erase(std::remove(v.begin(), v.end(), iValue), v.end());
But that should be far slower since for a random existent element, it's n/2 moves and n compares. My version is 1 move and n/2 compares.
Surely there's a better way to do this in "the modern idiom" than erase-remove-idiom? And if not why not?
There aren't a ready-made function for every niche use case in the standard library. Unstable remove is one of the functions that is not provided. It has been proposed (p0041r0) a while back though. Likewise, there are also no special versions of algorithms for the special case of vectors that do not contain duplicates.
So, you'll need to implement the algorithm yourself if you wish to use an optimal algorithm. There is
std::find
for linear search. After that, you only need to assign from last element and finally pop it off.