Check times a value is next to the same value in an array

Question

Lets say I have this array on C#:

int myList = {1,4,6,8,3,3,3,3,8,9,0}

I want to know if a value (lets say from 0-9) is next to itself in the list and how many times. In this case, the value 3 is next to itself and it has 4 repetitions. If I have a list {0,1,2,3,4,5,5,6,7} the value 5 is next to itself and has 2 repetitions.

Repetitions have a limit of 5. No value can be repeated more than 5 times. The far I went is making if statements, but I know there's a better way of doing it.

Answer 1

Best Answer

Answer by cjdev · Aug 05, 2015 at 09:08 PM

You could use a function like this:

 public int GetRepetitions(int[] myList, int value)
 {
     int repetitions = 0;
     for (int i = 0; i < myList.Length; i++)
     {
         if ((myList[i] == value) && ((i == 0 ? false : myList[i - 1] == value) ||
              (i == myList.Length - 1 ? false : myList[i+1] == value)))
         {
             repetitions++;
         }
     }
     return repetitions;
 }

In case you haven't seen it, the a ? b : c operator just means if a then b else c.

Edit: hehe, too slow, either will work.

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DarkSlash · Aug 05, 2015 at 09:27 PM 0

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This doesn't work well if the list is {1,2,3,3,4,5,6,3,3,3} it prints 5 when it should print or 2 or 3.

Nevertheless I think I can change to make it work as I need! THANK YOU!!!

Can you explain me better the if? it checks the previous value if not the first and the next value if not the last?

cjdev · Aug 05, 2015 at 09:46 PM 0

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The ? : thing is called a ternary operator. Basically it's just an inline if then else statement, so if the first part before the question mark is true then you use the statement on the left of the colon, otherwise you use the statement on the right of the colon if it's false.

DarkSlash · Aug 05, 2015 at 09:48 PM 0

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I know the ?, just the if, but i get it! Thanks! :)

Answer 2

Answer by IgorAherne · Aug 05, 2015 at 08:59 PM

basic forloop will do

 using System;

 void Start(){
     int[] myArray = new int[]{1,1,1,3,3,3,3};
     Debug.Log(howManyRepetitionsAfterFirstOccurance(ref myArray, 3) );
 }


 int howManyRepetitionsAfterFirstOccurance(ref int[] array2Inspect, int value2Check){ //pass array by reference (don't copy it over, just point your finger at the one to work with
    startingPos = Array.IndexOf(array2Inspect, value2Check) //get the index of the first occurance of the number you need
    int repetitions = 0;

       for(int i = startingPos; i < array2Inspect.Length; i++){  //see if its present once or more in the array
         int value_at_cell = array2Inspect[ i ];      

         if (startingPos == -1 ||  value_at_cell != value2Check) break;

         repetitions++;
    }


    return  repetitions;
 }

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DarkSlash · Aug 05, 2015 at 09:03 PM 0

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Thanks! That should work in the case the list isn't something like {3,1,2,3,3,3,3,3} how do you fix that?

NoseKills · Aug 05, 2015 at 09:15 PM 0

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To "fix" that you'd first need to design how you want it to work in that case. Return the length of the longest set, last set, first found, length of all sets combined ...

IgorAherne · Aug 05, 2015 at 09:18 PM 0

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return 0 if the startingPos is not -1

iterate through the array starting from the startingPos and keep bumping the number of repetitions. If suddenly the value does not equal to the one you wanted, then the repetition has ended.

Store this accumulated result in a biggestRepetitions if it is smaller than the current repetitions. reset repetitions back to zero keep going until you reach the end of the array and return biggestRepetitions.

Answer 3

Answer by NoseKills · Aug 05, 2015 at 09:58 PM

Already answered, but i'll just leave this here for fun :)

 void countNumber(int[] array, int value, out int longest, out int cumulative, out int first, out int last)
 {
     cumulative = longest = first = last = 0;
 
     int lastIndex = array.Length - 1;
     int currentStreak = 1;
     bool wasMatch = false;
 
     for(int i = 0; i <= lastIndex; i++)
     {  
         bool isMatch = array[i] == value;
 
         if (wasMatch)
         {
             if (isMatch)
             {
                 currentStreak++;
             }
 
             bool endOfStreak = !isMatch || i == lastIndex;
 
             if (endOfStreak && currentStreak > 1)
             {
                 if (currentStreak > longest) longest = currentStreak;
 
                 if (first == 0) first = currentStreak;
 
                 last = currentStreak;
                 cumulative += currentStreak;
                 currentStreak = 1;
             }
         }
         wasMatch = isMatch;
     }
 }

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Answer 4

I have this solution which can pick the consecutive repeated elements (even if they are repeated itself too).

e.g., cases like:

{ 1, 4, 3, 6, 6, 8, 3, 3, 3, 3, 8, 9, 0 }; // Here 6 and 3 are repeated

{ 1, 4, 3, 3, 6, 6, 8, 3, 3, 3, 3, 8, 9, 0 }; // Here 6 repeated once and 3 repeated twice

Sample Code:

 int[] myList = new int[] { 1, 4, 3, 3, 6, 6, 8, 3, 3, 3, 3, 8, 9, 0 };
 Dictionary<int, List<int>> groupDict = new Dictionary<int, List<int>>();
 string characters = string.Join("", myList.ToArray());
 
 for (int i = 0; i < characters.Length; i++)
 {
     int cInt = int.Parse(characters[i].ToString());
     MatchCollection mColl = Regex.Matches(characters.Substring(i), "^" + characters[i] + "{2,}");
     if (mColl.Count > 0)
     {
            if (!groupDict.Keys.Contains(cInt))
            {
                 groupDict.Add(cInt, new List<int>());
            }
 
            groupDict[cInt].Add(mColl[0].Length);
            i += mColl[0].Length - 1;
           }
      }
  }

For first case it will show you: (in-memory result)

 6 -> 2
 3 -> 4

For second case it will show you: (in-memory result)

 6 -> 2
 3 -> 2, 4

Hope it is useful for you.

Check times a value is next to the same value in an array

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