在整数数组中查找前3个最大重复数

Question

I want to find the top 3 maximum repeated numbers in a Integer array?

Below is the piece of code which I have tried but I couldn't find the desired result:

static void Main(string[] args)
    {

      int[,] numbers = {
                           {1, 2, 0, 6 },
                           {5, 6, 7, 0 },
                           {9, 3, 6, 2 },
                           {6, 4, 8, 1 }
                        };           
        int count = 0;
        List<int> checkedNumbers = new List<int>();
        foreach (int t in numbers)
        {
            if (!checkedNumbers.Contains(t))
            {
               foreach (int m in numbers)                   
               {
                   if (m == t)                        
                      {   
                         count++;
                      }
                }
                Console.WriteLine("Number {0} is Repeated {1} Times ", t, count);
               count = 0;
                checkedNumbers.Add(t);
            }           
       }
        Console.ReadLine();
    }

Answer 1

You can use GroupBy from LINQ then OrderByDescending based on count in each group:

var result = list.GroupBy(i => i)
                 .OrderByDescending(g => g.Count())
                 .Select(g => g.Key)
                 .Take(3);

---

Edit: With your code, you can use OfType to flatten your matrix then use the code above:

int[,] numbers = {
                       {1, 2, 0, 6 },
                       {5, 6, 7, 0 },
                       {9, 3, 6, 2 },
                       {6, 4, 8, 1 }
                 };

var list = numbers.OfType<int>();

Answer 2

int[] numbers = {1, 2, 3, 5, 6, 32, 2, 4, 42, 2, 4, 4, 5, 6, 3, 4};
var counts = new Dictionary<int, int>();
foreach (var number in numbers)
{
    counts[number] = counts[number] + 1;
}
var top3 = counts.OrderByDescending(x => x.Value).Select(x => x.Key).Take(3);

Answer 3

Hint:

You can do this with the help of LINQ.
This is the code to find most frequest occuring element:-

List<int> list = new List<int>() { 1,1,2,2,3,4,5 };

// group by value and count frequency
var query = from i in list
            group i by i into g
            select new {g.Key, Count = g.Count()};

// compute the maximum frequency
int frequency = query.Max(g => g.Count);

// find the values with that frequency
IEnumerable<int> modes = query
                              .Where(g => g.Count == frequency)
                              .Select(g => g.Key);

// dump to console
foreach(var mode in modes) {
    Console.WriteLine(mode);
}

In the same manner you can find the other two also.

Answer 4

I see that none of the existing answers provide an explanation, so I will try to explain.

What you need to do is to count how many times each item appears in the array. To do that, there are various methods (dictionaries, linq etc). Probably it would be easiest to use a dictionary which contains the number, and how may times it appeared:

int numbers[] = {1, 3, 6, 10, 9, 3, 3, 1, 10} ;
Dictionary<int, int> dic = new Dictionary<int, int>();

Now iterate through every element in numbers, and add it to the dictionary. If it was already added, simply increase the count value.

foreach (var i in numbers)
{
    dic[i]++; // Same as dic[i] = dic[i]+1;
}

The dictionary will automatically adds a new item if it doesn't exist, so we can simply do dic[i]++;

Next, we need to get the highest 3 values. Again, there are many ways to do this, but the easiest one would be to sort it.

var sorted_dic = dic.OrderByDescending(x => x.Value);

Now the first 3 items in sorted_dic are going to be the 3 values you are looking for. There are various methods to get only these 3, for example using the Take method:

var first_3 = sorted_dic.Take(3);

Now you can iterate through these 3 values, and for example print them on the screen:

foreach (var i in first_3)
{
    Console.Write("{0} appeared {1} times.", i.Key, i.Value);
}