How to find the duplicate items in a list?

[cathy25]

Hi,
My requirement is to check for duplicate items in a list of 16 strings.They will be entered by users like this...Item1,It em2,Item3....It em16. I need to check for the repeated items if any exists and need to reset it to zero or null.
Could any body point me in a direction to write the logic in C#?

Thanks,
Cathy

[PRR]

@cathy25
For any list look for Items.Contains method ...If Contains() returns false you can add else no...

string[] ss ={ "1","1","1"};
            List<string> myList = new List<string>();
 
 
            foreach (String s in ss)
            {
                if (!myList.Contains(s))
                {
                 myList.Add(s);
                }
            }
 
            foreach (String s in myList)
            {
                Console.WriteLine(s);
            }
 

[cathy25]

Thanks for your reply. But, in my case, I don't have any lists.
we are loading the user input as follows

for(int i=1;i<=15;i++)
{
string FirstItem=ID1.t ext
}

...like this. Then how can I use this in my foreach statment?

TIA

[PRR]

@cathy25
You will have to explain more... post some sample code....

[cathy25]

for (int i = 1; i <= 15; i++)
{
string firstId = FirstItemId[i].ToString();
string secondId = FirstItemId[i+1].ToString();
if (firstId == secondId)
{
MessageBox.Show ("Duplicate Item exists....,Syst em is resetting it to blank! If you would like to change it, open the form again");
SecondItemId='' ;
break;
}
I know this code checks every 2 items sequentially and returns the result. But, I need to check all the 16 items for duplication.

[PRR]

@cathy25
Instead of using string array[] "FirstItemI d" use List<String>... that way you wont have duplicate items....
Put your "Item1,Item2,It em3....Item16" in list<string> .. use Contains() method to see if the value already exists...Refer the earlier code i posted above ....

[mldisibio]

I believe cathy25 wants to maintain an array of 16 items, but have any duplicates blanked out.
You can follow DeepBlue's logic slightly modified:

You have your first array already, FirstItemId which is string[16].
Make a second, empty string array:

string[] nonDuplicateArray = new string[16];

Then fill it, checking for duplictes:

for(int i=0; i<16; i++){
  // For each item in original array, if my new array already has it, 
  // make it a blank, otherwise, copy it to the new array
  if(Array.IndexOf(nonDuplicateArray, FirstItemId[i]) > -1)
    nonDuplicateArray[i] == "";
  else
    nonDuplicateArray[i] = FirstItemId[i];
}

now return your second array.

return nonDuplicateArray;

[cathy25]

Yes! it worked. Thanks mldisiblo.