C++ algorithm like python's 'groupby'

Question

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

Answer 1

How about this?

template 
auto GroupBy(const std::vector& instances, const FieldSelectorUnaryFn& fieldChooser)
{
    StructType _;
    using FieldType = decltype(fieldChooser(_));
    std::map> instancesByField;
    for (auto& instance : instances)
    {
        instancesByField[fieldChooser(instance)].push_back(instance);
    }
    return instancesByField;
}

and use it like this:

auto itemsByX = GroupBy(items, [](const auto& item){ return item.x; });