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I tried to find 2 or more same elements from array x and then that duplicate to add into new array Y

So if i have in x array number like: 2,5,7,2,8 I want to add numbers 2 into y array

int[] x = new int[20];
        Random rnd = new Random();
        int[] y = new int[20];
        int counter = 0;


        for (int i = 0; i < x.Length; i++)
        {
            x[i] = rnd.Next(1, 15);

            for (int j=i+1;  j< x.Length; j++)
            {
                if (x[i] == x[j]) 
                {

                    y[counter] = x[i];
                    Console.WriteLine("Repeated numbers are " + y[counter]);
                    counter++;
                }
                else
                {
                    Console.WriteLine("There is no repeated numbers, numbers that are in x are  " + x[i]);
                }
                break;
            }
        }

But having problems with that, when it come to the if loop it doesn't want to proceed with executing if loop (even if condition is true)

If someone could give me some suggestion, that would be helpful, thank you

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3
  • Your first error is that you are using a break statement inside your second for loop so the loop is always executing only once Commented May 25, 2018 at 6:47
  • Hello, looking at some other posts of yours it appears you're a beginner trying to get to grips with software development (that's great, and kudos BTW!). I think questions like this are a better fit for other communities (like /r/learnprogramming on Reddit), because here on StackOverflow this kind of question tends to get flagged and you'll might get some not so friendly comments (or answers suggesting you should just use Linq, which would of course solve the problem but would not teach you the basics). Just a thought. Commented May 25, 2018 at 6:48
  • No the first error is that he is filling the x[] array (the x[i] = rnd.Next(1, 15);) and then looking in the uninitialized elements (the for (int j=i+1; j< x.Length; j++)) Commented May 25, 2018 at 6:49

6 Answers 6

Reset to default
4

There are various logical errors in your use of for. You should work more on your logic, because while libraries can be learnt by rote, logical errors are more something that is inside you.

int[] x = new int[20];
Random rnd = new Random(5);

// You don't know the length of y! 
// So you can't use arrays
List<int> y = new List<int>();

// First initialize
for (int i = 0; i < x.Length; i++)
{
    x[i] = rnd.Next(1, 15);
}

// Then print the generated numbers, otherwise you won't know what numbers are there
Console.WriteLine("Numbers that are in x are: ");
for (int i = 0; i < x.Length; i++)
{
    Console.WriteLine(x[i]);
}

// A blank line
Console.WriteLine();

// Then scan
for (int i = 0; i < x.Length; i++)
{
    for (int j = i + 1; j < x.Length; j++)
    {
        if (x[i] == x[j])
        {
            y.Add(x[i]);
            Console.WriteLine("Repeated numbers is " + x[i]);
        }
    }
}

// Success/failure in finding repeated numbers can be decided only at the end of the scan
if (y.Count == 0)
{
    Console.WriteLine("There is no repeated numbers");
}

I've put some comments in the code (plus the changes)

And for debugging purpose, I suggest you use a fixed Random sequence. new Random(5) (or any other number) will return the same sequence every time you launch your program.

Note that if there are multiple repetitions of a number, like { 4, 4, 4 } then the y array will be { 4, 4 }

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1 Comment

Thank you ,this helped, finally got where im making mistakes all the time!!
2

at first: why do u use the 'break;' ?

second: in the first for - loop u assign a random number to x[i] but then in the nested second loop u already ask x[j] to check for same values (but that doesn't exist yet)

there are so many ways to check if values are equal, but i like your approach: so what i would suggest:

make a for - loop and assign all the random numbers to int[] x

then think again how u can evaluate x[0] = x[1] or x[2] or x[3] ...

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0

Try to use Linq to find the duplicate in the Array

int[] x = new int[] { 2, 5, 7, 2, 8 };
int[] y;

var result = x.GroupBy(item => item)
              .Select(grp => new { key = grp.Key, Count = grp.Count() });

y = result.Where(res => res.Count > 1).Select(res => res.key).ToArray();
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Comments

0 
int[] array = new int[5] {1,2,3,4,4};
List<int> duplitcateList = array.Where(x => array.Where(y => y == x).Count() > 1).Distinct().ToList();

or you can replace last line of above code with below.

List<int> duplitcateList = array.
    GroupBy(x => x).Where(g => g.Count() > 1).Select(g => g.Key).ToList();

above code is using Linq.

suppose your first array (in question x) is array. Linq will first check for all elements in to list which occur more then once, and select them distinctly and store it to duplicateList

if you need an array at the, you can simply convert this list to array by doing this,

int[] yArray = duplitcateList.ToArray();
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4 Comments

OP is clearly a begginer so how you think this is going to help
I am adding description.
The problem isn't the description the problem is that you are giving a LINQ solution to begginer so I doubt it that the OP will understand it, maybe a better answer would be to show the OP where the mistakes are in the code he posted
@SlavenTojić I think today or tomorrow, he will learn Linq, so why not form today.
0

Make use of linq in your code , as below 

//first populate array x 
var duplicates= xArray.GroupBy(x => x)
              .Where(g => g.Count() > 1)
              .Select(y => y.Key)
              .ToArray();

linq query above make use of groupby and find duplicate i.e. element occuring more then one time in you array and then you select those element and return result

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9 Comments

OP is clearly a begginer so how you think this is going to help
@SlavenTojić - updated my answer hope that helps , linq is one of important feature its better to learn now its time :)
@SlavenTojić - so you say never learn new thing like linq , and do update messy /complicated code ...??
I don't think your solution is bad, but maybe a better answer would be to show the OP where the mistakes are in the code he posted
@SlavenTojić, I may be wrong but answer are not exactly for op on So. no matter the question answer are a little bit more for the future. Does this answer the question? Is it clear? Does it need explanation?
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0

I think this will will be the most understandable solution without complicated extension methods:

int[] x = new int[20];
// there can be at most 10 duplicates in array of length of 20 :)
// you could use List<int> to easily add elements
int[] y = new int[10];
int counter = 0;
Random rnd = new Random();
// fill the array
for (int i = 0; i < x.Length; i++)
    x[i] = rnd.Next(1, 15);
// iterate through distinct elements,
// otherwise, we would add multiple times duplicates
foreach (int i in x.Distinct())
    // if the count of an elements is greater than one, then we have duplicate
    if(x.Count(n => n == i) > 1)
    {
        y[counter] = i;
        counter++;
    }
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