如何使用LINQ获取int数组中的前3个元素？

Question

I have the following array of integers:

int[] array = new int[7] { 1, 3, 5, 2, 8, 6, 4 };

I wrote the following code to get the top 3 elements in the array:

var topThree = (from i in array orderby i descending select i).Take(3);

When I check what's inside the topThree , I find:

{System.Linq.Enumerable.TakeIterator}
count:0

What did I do wrong and how can I correct my code?

Answer 1

How did you "check what's inside the topThree"? The easiest way to do so is to print them out:

using System;
using System.Linq;

public class Test
{
    static void Main()        
    {
        int[] array = new int[7] { 1, 3, 5, 2, 8, 6, 4 };
        var topThree = (from i in array 
                        orderby i descending 
                        select i).Take(3);

        foreach (var x in topThree)
        {
            Console.WriteLine(x);
        }
    }
}

Looks okay to me...

There are potentially more efficient ways of finding the top N values than sorting, but this will certainly work. You might want to consider using dot notation for a query which only does one thing:

var topThree = array.OrderByDescending(i => i)
                    .Take(3);

Answer 2

Your code seems fine to me, you maybe want to get the result back to another array?

int[] topThree = array.OrderByDescending(i=> i)
                      .Take(3)
                      .ToArray();

Answer 3

Its due to the delayed execution of the linq query.

As suggested if you add .ToArray() or .ToList() or similar you will get the correct result.

Answer 4

int[] intArray = new int[7] { 1, 3, 5, 2, 8, 6, 4 };            
int ind=0;
var listTop3 = intArray.OrderByDescending(a=>a).Select(itm => new { 
    count = ++ind, value = itm 
}).Where(itm => itm.count < 4);