Remove only first met element in stl list

Question

I've got a list of elements stored in stl c++ list. How to remove only one of repeating values?

#include <list>
int main() {
    std::list<int> listOfInts({ 1, 2, 3, 3, 4, 5 });
    listOfInts.remove(3);
    return 0;
}

My list will now look like this: 1, 2, 4, 5. Is there a way to make it look like this: 1, 2, 3, 4, 5?

I know it might be very easy, but it's my first time with stl list and I appreciate all tips.

See https://stackoverflow.com/questions/1041620/whats-the-most-efficient-way-to-erase-duplicates-and-sort-a-vector — Quarra, Dec 07 '20 at 13:02
Does this answer your question? [What's the most efficient way to erase duplicates and sort a vector?](https://stackoverflow.com/questions/1041620/whats-the-most-efficient-way-to-erase-duplicates-and-sort-a-vector) — Quarra, Dec 07 '20 at 13:05
@Quarra: Removing duplicates will reduce the number of copies **to** one, not **by** one. E.g. if the input was `1,2,3,3,3,4,5`, removing only the first occurrence of `3` would leave `1,2,3,3,4,5` - still a duplicate. — MSalters, Dec 07 '20 at 13:13

score 3 · Answer 1 · answered Dec 07 '20 at 13:10

3

Use the standard algorithm std::find

#include <list>
#include <iterator>
#include <algorithm>

//...
auto it = std::find( std::begin( listOfInts ), std::end( listOfInts ), 3 );

if ( it != std::end( listOfInts ) ) listOfInts.erase( it );

answered Dec 07 '20 at 13:10

Vlad from Moscow

301,070
26
186
335

Don't actually need all those `std::` there. After `std::list listOfInts` ADL will find the `std` namespace. – MSalters Dec 07 '20 at 13:15
Works perfectly, now it's time to analyze this piece of code, thank you! – sra.mik Dec 07 '20 at 13:16
3

@MSalters Using qualified names makes the code more readable. – Vlad from Moscow Dec 07 '20 at 13:18
that's quite the subjective statement, personally I think it's way more readable without namespace clutter – Yamahari Dec 07 '20 at 13:47
Is there a reason to prefer `std::begin(listOfInts)` over `listOfInts.begin()`? – Nathan Pierson Dec 07 '20 at 15:03
@NathanPierson Using a more general approach is better. In this case you can for example substitute the list for an array. – Vlad from Moscow Dec 07 '20 at 15:15
well as I said, you can't really speak from my perspective – Yamahari Dec 07 '20 at 16:21

score 0 · Answer 2 · answered Dec 07 '20 at 14:20

You can do as

#include <list>
#include <algorithm>

using namespace std;

int main() {
    list<int> listOfInts({ 1, 2, 3, 3, 4, 5 });

    auto itr = find(listOfInts.begin(), listOfInts.end(), 3);

    if (itr != listOfInts.end()) {
        listOfInts.erase(itr);
    }

    return 0;
}

Remove only first met element in stl list

2 Answers2