Mapping a vector to specific range

user_7982776 0
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I have a standard vector contains, for example, the following elements

[-6, -7, 1, 2]

I need to map these elements to the range from 1 to 4. i.e I need the vector to be like this

[2, 1, 3, 4]

Note that: the smallest value in the first vector (-7) was mapped to the smallest value in the second vector (1). How can I achieve that with STL?

vector stl c++
3 Answers

With range-v3:

std::vector<int> v{-6, -7, 1, 2};
auto res = ranges::view::ints(1, 1 + (int)v.size()) | ranges::to_vector;

ranges::sort(ranges::view::zip(v, res));

Demo

user_26845390

With just the standard library as it exists in C++17 (or really, C++11), you make a vector of indices and sort it - using itself as a projection:

vector<int> idxs(values.size());
iota(idxs.begin(), idxs.end(), 1);
sort(idxs.begin(), idxs.end(), [&](int i, int j){
    return values[i-1] < values[j-1];
});

A different way of generating the indices would be to use generate_n:

vector<int> idxs;
generate_n(back_inserter(idxs),
    values.size(),
    [cnt=1]() mutable { return cnt++; });
// same sort()
user_20690640

Using a helper vector of pairs:

std::vector<int> a { -6, -7, 1, 2 };

std::vector<std::pair<int, int>> tmp;
for (int i = 0; i < (int) a.size(); ++i) {
    tmp.push_back({ a[i], i });
}

std::sort(tmp.begin(), tmp.end());

std::vector<int> b;
for (auto & x : tmp) {
    b.push_back(x.second + 1);
}

Demo

Using a helper priority_queue of pairs (to avoid explicit sorting):

std::vector<int> a { -6, -7, 1, 2 };

std::priority_queue<std::pair<int, int>> tmp;
for (std::size_t i = 0; i < a.size(); ++i) {
    tmp.push({ -a[i], i});
}

std::vector<int> b;
do {
    b.push_back(tmp.top().second + 1);
} while (tmp.pop(), !tmp.empty());

Demo

user_40399760
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