Counting the number of times a value appears in an array

Question

So what's a good, simple algorithm to create a loop in C# where every time a certain value appears in an array it adds 1 to a counter in another array?

For example I have this:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication22
{
    class Program
    {
        const int SIZE = 12;

        static void Main(string[] args)
        {
            int[] numbers = new int[SIZE] {5, 5, 5, 7, 7, 7, 9, 7, 9, 9, 9, 1};
           string[] letters = new string[SIZE] { "m", "m", "s", "m", "s", "s", "s", "m", "s", "s", "s", "s" };
            int[] values = new int[SIZE] {15, 22, 67, 45, 12, 21, 24, 51, 90, 60, 50, 44};
            string[] status = new string[SIZE] { "f", "m", "f", "a", "m", "f", "f", "f", "m", "f", "m", "f" };

            int[] Count = new int[4];
            int x = 0;
            int i = 0;

            for (i = 0; i < SIZE - 1; i++)
            {
                if (numbers[i] > 0 && numbers[i] < SIZE)
                {
                    x = Count[i];
                    Count[x]++;
                }
            }

            for (i = 0; i < 4; i++)
            {
                Console.WriteLine("{0}", Count[4]);
            }
        }
    }
}

I am only counting the number of times 4 numbers appear in the numbers array. Someone suggested I use the method in the first loop but it doesn't seem to be working and creates an error that the index is out of bounds in the array. I want to display the number of times each of those numbers(5, 7,9 and 1) appear in 4 rows.

EDIT: Without using LINQ or any other fancy thing like Dictionary or whatever.

Answer 1

   int number = 0;
   int[] arr = {1,7,8,8,8,8,1,1,2,1,5,1,2,5,5,5,5,5,};
   bool containsNumber = false;
   List<int> existingElements = new List<int>();
     
   for(int i = 0; i < arr.Length; i++)
   {
    for(int j = 0; j < existingElements.Count; j++){
      if(arr[i] == existingElements[j]) {
            containsNumber = true;
            break;
         }
    }
     
     
     if(containsNumber)
     {
       containsNumber = false;
       continue;
     }
       
     for(int k = 0; k < arr.Length; k++)
      {
        if(arr[i] == arr[k])
        {
            number++;
        }

      }
     existingElements.Add(arr[i]);
     Console.WriteLine ("The number "+ arr[i] +" appears "+ number +" Times");
     number = 0;
     
   }
 

Answer 2

I think the question hasn't been answered without using lists, LINQ or Dictionary so here is my suggestion:

using System;
using System.Collections.Generic;
//using System.Linq;
using System.Text;

class Program
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine()); // the size of the array
        int[] ints = new int[n]; //an array to store the items, integers in this case
        int[] freq = new int[n]; //an array to store the frequency of each element with the same index

        for (int i = 0; i < n; i++) // a loop that takes each element on a new row
        {
            ints[i] = int.Parse(Console.ReadLine());
        }

        for (int j = 0; j < n; j++) // loops to iterate through the ints array and pick up the
                                    // frequencies and store them in the freq array
        {
            for (int k = 0; k < n; k++)
            {
                if (ints[j] == ints[k] && k != n)
                {
                    freq[j]++;
                }
            }
        }

        int indexAtMax = freq.ToList().IndexOf(freq.Max()); //this picks up the index of the first maximum count
        int mostFrequentNumber = ints[indexAtMax]; // the actual number behind the same inex in the ints array
        int frequencyOfRepeating = freq[indexAtMax]; // the actual number of the frequency 

        Console.WriteLine($"The most frequent number is:{mostFrequentNumber} and it repeats {frequencyOfRepeating} times)");
    }
}

Answer 3

 static void Main(string[] args)
        {
            int[] arr = new int[] { 45, 34, 23, 67, 10, 99,99,10 };
            foreach(int i in arr.Distinct())
            {
                int count = occurance(arr,i);
                Console.WriteLine(i + "-Occurred For :" + count);
            }
            
            Console.ReadLine();
        }
        public static int occurance(int[] arr,int x)
        {
            int count = 0;
            foreach(int num in arr)
            {
                if(x==num)
                {
                    count++;
                }
            }
            return count;
        }
    }

Answer 4

This is the naive Solution for finding " Counting the number of times a value appears in an array " Idea : Build a Hash map in Array Solution :

using System.Collections.Generic;
using System.Text;

namespace GetArrEleFrequency
{
    class Program
    {
      static int[] Arr = new int[5] { 3, 3, 0, 2, 0 };
      static int[] Key = new int[5];
      static int[] value = new int[5];
      static void Main(string[] args)
      {
         int keyItr = -1, ValueItr = -1, tempIndex = 0, tempValue = 0;
         for (int i=0; i <= Arr.Length-1;i++) {
              if (!(isPresent(Arr[i]))) {
                   keyItr += 1;ValueItr += 1;
                   Key[keyItr] = Arr[i];
                   value[ValueItr] = 1;
             } else {
                   
                   value[tempIndex] = value[getIndex(Arr[i])] + 1;
            }
        }
        for (int i=0;i<=Key.Length-1;i++) {
              Console.WriteLine(Key[i] + "-" + value[i]);
        }
        Console.ReadKey();
     }
     public static Boolean  isPresent(int num) {
      Boolean temp = false;
      for (int i=0; i <= Key.Length-1;i++) {
        if (Key[i] == num) {
              temp = true;
              break;
        } else {
              temp = false;
        }
     }
     return temp;
   }
   public static int getIndex(int num) {
       int temp = 0;
       for (int i=0;i<=Key.Length-1;i++) {
             if (Key[i] == num) {
               break;
             } else {
             temp += 1;
       }
  }
  return temp;
   }
 }
}

Output :

    3 - 2
    0 - 2
    2 - 1
    0 - 0
    0 - 0

Answer 5

I used Regex for my solution since I only had three values.

String results = "" + one.ToString() + " " + two.ToString() + " " + three.ToString();
int count1 = Regex.Matches(results, @one.ToString()).Count;
int count2 = Regex.Matches(results, @two.ToString()).Count;
int count3 = Regex.Matches(results, @three.ToString()).Count;

Seems 'hacky', but worked for me. It'll work with strings or numbers but only if you're working with a few values. Pretty efficient in that case. If not, I think the other answer would be a better option.

Answer 6

You're getting an index out of bounds error because of this section:

for (i = 0; i < SIZE - 1; i++)
{
    if (numbers[i] > 0 && numbers[i] < SIZE)
    {
        x = Count[i];

Notice that you're iterating through 0 to SIZE - 1 (11) when Count only has a size of 4.

---

You can do this task pretty easily with LINQ though.

int[] numbers = new int[SIZE] { 5, 5, 5, 7, 7, 7, 9, 7, 9, 9, 9, 1 };

var count = numbers
    .GroupBy(e => e)
    .Where(e => e.Count() == 4)
    .Select(e => e.First());

So it groups the numbers by their value, we then refine the list to only include groups of 4, then select the first of each to be left with a collection of ints.

---

Here is a non-LINQ based solution using a Dictionary to store the count of numbers.

int[] numbers = new int[SIZE] { 5, 5, 5, 7, 7, 7, 9, 7, 9, 9, 9, 1 };
var dictionary = new Dictionary<int, int>();
var numbersWithFour = new List<int>();

foreach (var number in numbers)
{
    if (dictionary.ContainsKey(number))
        dictionary[number]++;
    else
        dictionary.Add(number, 1);
}

foreach (var val in dictionary)
{
    if (val.Value == 4)
    {
        numbersWithFour.Add(val.Key);
    }
}

---

With a little modification to your program you can get some results.

int[] numbers = new int[SIZE] { 5, 5, 5, 7, 7, 7, 9, 7, 9, 9, 9, 1 };
string[] letters = new string[SIZE] { "m", "m", "s", "m", "s", "s", "s", "m", "s", "s", "s", "s" };
int[] values = new int[SIZE] { 15, 22, 67, 45, 12, 21, 24, 51, 90, 60, 50, 44 };
string[] status = new string[SIZE] { "f", "m", "f", "a", "m", "f", "f", "f", "m", "f", "m", "f" };

// Set the size of Count to maximum value in numbers + 1
int[] Count = new int[9 + 1];
int x = 0;
int i = 0;

for (i = 0; i < SIZE - 1; i++)
{
    if (numbers[i] > 0 && numbers[i] < SIZE)
    {
        // Use value from numbers as the index for Count and increment the count
        Count[numbers[i]]++;
    }
}

for (i = 0; i < Count.Length; i++)
{
    // Check all values in Count, printing the ones where the count is 4
    if (Count[i] == 4)
        Console.WriteLine("{0}", i);
}

Output:

7
9

Answer 7

Use LINQ to do the work

using System.Linq;

var numQuery =
        from num in numbers
        where num == 5
        select num;

Console.WriteLine("Count of 5: " + numQuery.Count);

Or use the method syntax

var numQuery = numbers.Where(num => num == 5);
Console.WriteLine("Count of 5: " + numQuery.Count);

See here for the overview and here for query vs method-syntax.
Found a sample for GroupBy, look here.

Answer 8

your count array has 4 fields ...

one with the index 0, 1, 2 and 3

so what will happen if a number like 4 (or greater) happens to be counted? yor code tries to access index 4 ... which does not exist ...