在向量中找到最接近的值 [英] Find Closest Value in Vector

问题描述

我要完成的工作是遍历一个double值的向量，并返回最接近的double的向量位置.我对此有两个问题.

What I am trying to accomplish is iterating through a vector of double values and returning the vector position of the closest possible double. I am having two issues with this.

1. 当尝试使用lower_bound()在向量中找到最接近的双精度值时，如果我输入1，则仅会收到零以外的值.

1. When attempting to find the closest double value in the vector using lower_bound(), i only receive a value other than zero if I enter 1.

我不确定如何使用lower_bound返回矢量位置而不是双精度值.

I am not sure how to use lower_bound to return a vector position instead of a double value.

这是我正在使用尝试的代码的三个主要文件

Here is my three main files I am using with attempted code

Convert.cpp

Convert.cpp

double Convert::convertmVtoK(double value)
{
    double conversion = *std::lower_bound(mV.begin(), mV.end(), value);
    cout<<"This is conversion mV to K"<<" "<< conversion;
}

double Convert::convertKtomV(double value)
{
    double conversion = *std::lower_bound(mV.begin(), mV.end(), value);
    cout<<"This is conversion K to mV"<<" "<< conversion;
}

Conversion.h

Conversion.h

class Convert
{
    public:
        Convert();
        virtual ~Convert();
        double convertmVtoK(double mV);
        double convertKtomV(double K);
        void readFile();

    protected:

    private:
        std::ifstream inFile;
        std::vector<double> kelvin,mV,sensitivity;
        double tempKelvin,tempmV,tempSensitivity;
};

#endif // CONVERT_H

Main.cpp

#include "Convert.h"
#include <stdio.h>
#include<fstream>
#include<iostream>


int main()
{
    Convert convert;
    convert.readFile();
   convert.convertmVtoK(2.0);
    convert.convertKtomV(5.000);

    return 0;
}

更新:所以我仍在尝试使用lower_bound().这是我更新的功能.

Update: So I am still attempting to use lower_bound(). Here is my updated function.

double Convert::convertmVtoK(double value)
{
    std::vector<double>::iterator pos;

    pos = std::lower_bound(mV.begin(), mV.end(), value);
    cout<<"This is conversion mV to K"<<" "<< kelvin[(pos-mV.begin())];
}

当前，如果我输入一个浮点值，我仍然无法接收正确的矢量值，它将返回0或[0]矢量值.

Currently the if I input a float value I am still not able to recieve the correct vector value, it either returns 0 or the [0] vector value.

更新2:文本值

1.4 1.644290    -12.5
1.5 1.642990    -13.6
1.6 1.641570    -14.8
1.7 1.640030    -16.0
1.8 1.638370    -17.1
1.9 1.636600    -18.3
2.0 1.634720    -19.3
2.1 1.632740    -20.3

推荐答案

您可以使用 min_element 和一个比较器，该比较器考虑了到value的距离:

// precondition: mV is not empty
double get_closest(double value) const
{
    assert(!mV.empty());
    auto it = std::min_element(mV.begin(), mV.end(), [value] (double a, double b) {
        return std::abs(value - a) < std::abs(value - b);
    });
    assert(it != mV.end());

    return *it;
}

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