Removing by index from a C++ vector using remove_if

I actually made an account only for this. Use awesomeyi answer. Is way cleaner.

int count = 0;
auto final = std::remove_if (data.begin(), data.end(), [&count](const double d) {
    return (count++) % 2;
});

The standard does say that the predicate is applied exactly last - first times. And remove_if works with ForwardIterators.

This implies that the predicate is applied only once in the same order they originally appear in the sequence.

Unless of course, the library is trolling you, by keeping internal copies of the ForwardIterator.

You can use pointer arithmetic to find the index of a specific element that std::remove_if passes to the predicate:

std::remove_if(data.begin(), data.end(),
               [&data](const double& d) { return (&d - &*data.begin()) % 2); });

Note that remove_if passes the result of dereferencing an iterator, and that's guaranteed to be a reference per Table 106 - Iterator requirements in the Standard.