mode.hpp

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#pragma once
 
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <utility>
 
#include "NumCpp/Core/Internal/StaticAsserts.hpp"
#include "NumCpp/Core/Internal/StdComplexOperators.hpp"
#include "NumCpp/Core/Internal/StlAlgorithms.hpp"
#include "NumCpp/Core/Types.hpp"
#include "NumCpp/NdArray.hpp"
 
namespace nc
{
    //===========================================================================
    // Method Description:
    template<typename dtype, typename HashFunction = std::hash<dtype>>
    NdArray<dtype> mode(const NdArray<dtype>& inArray, Axis inAxis = Axis::NONE)
    {
        const auto modeFunction =
            [](typename NdArray<dtype>::const_iterator iterBegin, typename NdArray<dtype>::const_iterator iterEnd)
        {
            std::unordered_map<dtype, int, HashFunction> counts{};
            auto                                         greatestCount = int{ 0 };
            dtype                                        mode{};
            for (auto iter = iterBegin; iter != iterEnd; ++iter)
            {
                const auto& value = *iter;
 
                if (counts.count(value) > 0)
                {
                    auto& count = counts[value];
                    ++count;
                    if (count > greatestCount)
                    {
                        greatestCount = count;
                        mode          = value;
                    }
                }
                else
                {
                    counts.insert({ value, 1 });
                }
            }
 
            return mode;
        };
 
        switch (inAxis)
        {
            case Axis::NONE:
            {
                NdArray<dtype> returnArray = { modeFunction(inArray.cbegin(), inArray.cend()) };
                return returnArray;
            }
            case Axis::COL:
            {
                NdArray<dtype> returnArray(1, inArray.numRows());
                for (uint32 row = 0; row < inArray.numRows(); ++row)
                {
                    returnArray(0, row) = modeFunction(inArray.cbegin(row), inArray.cend(row));
                }
 
                return returnArray;
            }
            case Axis::ROW:
            {
                return mode(inArray.transpose(), Axis::COL);
            }
            default:
            {
                THROW_INVALID_ARGUMENT_ERROR("Unimplemented axis type.");
                return {};
            }
        }
    }
 
    //============================================================================
    // Method Description:
    template<typename dtype>
    NdArray<std::complex<dtype>> mode(const NdArray<std::complex<dtype>>& inArray, Axis inAxis = Axis::NONE)
    {
        STATIC_ASSERT_ARITHMETIC(dtype);
 
        return mode<std::complex<dtype>, ComplexHash<dtype>>(inArray, inAxis);
    }
} // namespace nc