Count.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreTypes.h"
 
namespace Algo
{
    /**
     * Counts elements of a range that equal the supplied value
     *
     * @param  Input    Any iterable type
     * @param  InValue  Value to compare against
     */
    template <typename InT, typename ValueT>
    FORCEINLINE SIZE_T Count(const InT& Input, const ValueT& InValue)
    {
        SIZE_T Result = 0;
        for (const auto& Value : Input)
        {
            if (Value == InValue)
            {
                ++Result;
            }
        }
        return Result;
    }
 
    /**
     * Counts elements of a range that match a given predicate
     *
     * @param  Input      Any iterable type
     * @param  Predicate  Condition which returns true for elements that should be counted and false for elements that should be skipped
     */
    template <typename InT, typename PredicateT>
    FORCEINLINE SIZE_T CountIf(const InT& Input, PredicateT Predicate)
    {
        SIZE_T Result = 0;
        for (const auto& Value : Input)
        {
            if (Invoke(Predicate, Value))
            {
                ++Result;
            }
        }
        return Result;
    }
 
    /**
     * Counts elements of a range whose projection equals the supplied value
     *
     * @param  Input       Any iterable type
     * @param  InValue     Value to compare against
     * @param  Projection  The projection to apply to the element
     */
    template <typename InT, typename ValueT, typename ProjectionT>
    FORCEINLINE SIZE_T CountBy(const InT& Input, const ValueT& InValue, ProjectionT Proj)
    {
        SIZE_T Result = 0;
        for (const auto& Value : Input)
        {
            if (Invoke(Proj, Value) == InValue)
            {
                ++Result;
            }
        }
        return Result;
    }
}