C++ algorithm like python's 'groupby'

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再見小時候 2020-12-15 22:20

Are there any C++ transformations which are similar to itertools.groupby()?

Of course I could easily write my own, but I\'d prefer to leverage the idiomatic behavior

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执念已碎 (楼主)

2020-12-15 22:54

Eric Niebler's ranges library provides a group_by view.

according to the docs it is a header only library and can be included easily.

It's supposed to go into the standard C++ space, but can be used with a recent C++11 compiler.

minimal working example:

#include 
#include 
#include 
using namespace std;
using namespace ranges;

int main(int argc, char **argv) {
    vector l { 0,1,2,3,6,5,4,7,8,9 };
    ranges::v3::sort(l);
    auto x = l | view::group_by([](int x, int y) { return x / 5 == y / 5; });
    map> res;

    auto i = x.begin();
    auto e = x.end();
    for (;i != e; ++i) {
      auto first = *((*i).begin());
      res[first / 5] = to_vector(*i);
    }

    // res = { 0 : [0,1,2,3,4], 1: [5,6,7,8,9] }
}

(I compiled this with clang 3.9.0. and --std=c++11)

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