C# 查找最高数组值和索引

C# find highest array value and index

提问by Edmund Rojas

So I have an unsorted numeric array int[] anArray = { 1, 5, 2, 7 };and I need to get both the value and the index of the largest value in the array which would be 7 and 3, how would I do this?

所以我有一个未排序的数字数组int[] anArray = { 1, 5, 2, 7 };，我需要获取数组中最大值的值和索引，即 7 和 3，我该怎么做？

采纳答案by sa_ddam213

This is not the most glamorous way but works.

这不是最迷人的方式，但有效。

(must have using System.Linq;)

（必须有using System.Linq;）

 int maxValue = anArray.Max();
 int maxIndex = anArray.ToList().IndexOf(maxValue);

回答by Tom Hamming

If the index is not sorted, you have to iterate through the array at least once to find the highest value. I'd use a simple forloop:

如果索引未排序，则必须至少遍历数组一次才能找到最大值。我会使用一个简单的for循环：

int? maxVal = null; //nullable so this works even if you have all super-low negatives
int index = -1;
for (int i = 0; i < anArray.Length; i++)
{
  int thisNum = anArray[i];
  if (!maxVal.HasValue || thisNum > maxVal.Value)
  {
    maxVal = thisNum;
    index = i;
  }
}

This is more verbose than something using LINQ or other one-line solutions, but it's probably a little faster. There's really no way to make this faster than O(N).

这比使用 LINQ 或其他单行解决方案更冗长，但它可能要快一点。真的没有办法让它比 O(N) 更快。

回答by millimoose

The obligatory LINQ one^[1]-liner:

强制性的 LINQ one ^[1]-liner：

var max = anArray.Select((value, index) => new {value, index})
                 .OrderByDescending(vi => vi.value)
                 .First();

(The sorting is probably a performance hit over the other solutions.)

（排序可能是其他解决方案的性能损失。）

[1]:For given values of "one".

[1]：对于给定的“一”值。

回答by asr

int[] anArray = { 1, 5, 2, 7 };
// Finding max
int m = anArray.Max();

// Positioning max
int p = Array.IndexOf(anArray, m);

回答by Adam Nathan

anArray.Select((n, i) => new { Value = n, Index = i })
    .Where(s => s.Value == anArray.Max());

回答by GEEK

int[] numbers = new int[7]{45,67,23,45,19,85,64}; 
int smallest = numbers[0]; 
for (int index = 0; index < numbers.Length; index++) 
{ 
 if (numbers[index] < smallest) smallest = numbers[index]; 
} 
Console.WriteLine(smallest);

回答by Andreas

Output for bellow code:

以下代码的输出：

00:00:00.3279270 - max1 00:00:00.2615935 - max2 00:00:00.6010360 - max3 (arr.Max())

00:00:00.3279270 - max1 00:00:00.2615935 - max2 00:00:00.6010360 - max3 (arr.Max())

With 100000000 ints in array not very big difference but still...

数组中有 100000000 个整数，差别不大，但仍然......

class Program
    {
        static void Main(string[] args)
        {
            int[] arr = new int[100000000];

            Random randNum = new Random();
            for (int i = 0; i < arr.Length; i++)
            {
                arr[i] = randNum.Next(-100000000, 100000000);
            }
            Stopwatch stopwatch1 = new Stopwatch();
            Stopwatch stopwatch2 = new Stopwatch();
            Stopwatch stopwatch3 = new Stopwatch();
            stopwatch1.Start();

            var max = GetMaxFullIterate(arr);

            Debug.WriteLine( stopwatch1.Elapsed.ToString());


            stopwatch2.Start();
            var max2 = GetMaxPartialIterate(arr);

            Debug.WriteLine( stopwatch2.Elapsed.ToString());

            stopwatch3.Start();
            var max3 = arr.Max();
            Debug.WriteLine(stopwatch3.Elapsed.ToString());

        }



 private static int GetMaxPartialIterate(int[] arr)
        {
            var max = arr[0];
            var idx = 0;
            for (int i = arr.Length / 2; i < arr.Length; i++)
            {
                if (arr[i] > max)
                {
                    max = arr[i];
                }

                if (arr[idx] > max)
                {
                    max = arr[idx];
                }
                idx++;
            }
            return max;
        }


        private static int GetMaxFullIterate(int[] arr)
        {
            var max = arr[0];
            for (int i = 0; i < arr.Length; i++)
            {
                if (arr[i] > max)
                {
                    max = arr[i];
                }
            }
            return max;
        }

回答by Jeetendra Negi

int[] Data= { 1, 212, 333,2,12,3311,122,23 };
int large = Data.Max();
Console.WriteLine(large);

回答by Neil

Here are two approaches. You may want to add handling for when the array is empty.

这里有两种方法。您可能希望为数组为空时添加处理。

public static void FindMax()
{
    // Advantages: 
    // * Functional approach
    // * Compact code
    // Cons: 
    // * We are indexing into the array twice at each step
    // * The Range and IEnumerable add a bit of overhead
    // * Many people will find this code harder to understand

    int[] array = { 1, 5, 2, 7 };

    int maxIndex = Enumerable.Range(0, array.Length).Aggregate((max, i) => array[max] > array[i] ? max : i);
    int maxInt = array[maxIndex];

    Console.WriteLine($"Maximum int {maxInt} is found at index {maxIndex}");
}

public static void FindMax2()
{
    // Advantages: 
    // * Near-optimal performance

    int[] array = { 1, 5, 2, 7 };
    int maxIndex = -1;
    int maxInt = Int32.MinValue;

    // Modern C# compilers optimize the case where we put array.Length in the condition
    for (int i = 0; i < array.Length; i++)
    {
        int value = array[i];
        if (value > maxInt)
        {
            maxInt = value;
            maxIndex = i;
        }
    }

    Console.WriteLine($"Maximum int {maxInt} is found at index {maxIndex}");
}

回答by Joe Sonderegger

 public static class ArrayExtensions
{
    public static int MaxIndexOf<T>(this T[] input)
    {
        var max = input.Max();
        int index = Array.IndexOf(input, max);
        return index;
    }
}

This works for all variable types...

这适用于所有变量类型...

var array = new int[]{1, 2, 4, 10, 0, 2};
var index = array.MaxIndexOf();


var array = new double[]{1.0, 2.0, 4.0, 10.0, 0.0, 2.0};
var index = array.MaxIndexOf();