How Do I Search And Delete All The Duplicates In A String List Array

Question

1.67/5 (3 votes)

See more:

how do i search and delete all the duplicates in a string list array

for example:-

C#

List<string> st = new List<string> { "Hello", "World", "Welcome", "To", "Csharp", "Welcome", "World", "Hello", "To", "Hello" }; //Example string array

now duplicates should be deleted and remaining should be saved in the new list array and also i want the positions of the deleted items in new array

i did this in easy way but not by using list or genric collections

C#

using System;

namespace testing
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                int i = 0, j = 0, k = 0, n = 0, ctr = 0;

                Console.WriteLine("Please enter how many elements you want to enter..");
                n = int.Parse(Console.ReadLine());

                string[] a = new string[n];
                
                Console.WriteLine("Enter elements ");
                for (i = 0; i < n; i++)
                {
                    a[i] = Console.ReadLine();
                }

                // Here checking of duplicate elements
                for (i = 0; i < n; i++)
                {
                    for (j = i + 1; j < n; j++)
                    {
                        if (a[i] == a[j])
                        {
                            n = n - 1;
                            for (k = j; k < n; k++)
                            {
                                a[k] = a[k + 1];
                            }
                            ctr = 1;
                            j = j - 1;
                        }
                    }
                }


                if (ctr == 0)
                {
                    Console.WriteLine("Array does not contain duplicate elements");
                }
                else
                {
                    Console.WriteLine();
                    Console.WriteLine("After deletion the duplicate elements are :-");
                    for (i = 0; i < n; i++)
                    {
                        Console.WriteLine(a[i]);
                    }
                }
            }
            
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }

            Console.Read();
        }
    }
}

please help

Posted 10-Dec-15 6:43am

Palash Sachan

Updated 10-Dec-15 7:41am

v5

Add a Solution

Comments

Sergey Alexandrovich Kryukov 10-Dec-15 13:05pm

Why not blocking adding duplicates in first place?
—SA

Matt T Heffron 10-Dec-15 13:22pm

The nature of the question and your "please help ASAP" implies that this is likely homework that you've put off until "the last minute".
I'm sure I could come up with a solution in a few minutes, but that wouldn't really help you to learn.
You didn't show us any effort at trying to solve this yourself.
Use "Improve question" and show us what you have tried and where you are still having difficulty and you're likely to get good advice.

Palash Sachan 10-Dec-15 13:34pm

sir..u r correct..this is my homework..and i have tried this in easy way like this..see the ques again

Matt T Heffron 10-Dec-15 14:41pm

Your code doesn't actually do what you said you need.
You're using an array of a predetermined size when a List<string> would have been much simpler. (That's what you showed in your original statement of the problem.)
You aren't generating a "new list array" for the result. (a List is not an array. Confusing this is likely to cause you much grief in the future. List and array both implement the IList<T> interface which provides the indexed access ability.)
You never collect or report the index values of the deleted elements.
I usually don't like providing complete solutions to peoples' homework questions, but I've added Solution 3, below.
Remember, submitting any of these solutions as your own work is plagiarism! Learn from them and then submit your own solution.
(None of us will ever know if you submitted our work as yours. But you will know that you cheated!)

Palash Sachan 10-Dec-15 21:56pm

dear sir..i just made the program what i could make at this moment as i m new to c#..and so i was just asking to how to make it in as the list so that it can be simple..and NO i m not cheating on anyone sir..i m new to it..and i know that if i will do so than it will not be good for me as then i will not learn anything..and thanks for the help and ur solution sir :)

3 solutions

Solution 2

You can try something like this way:

C#

yourList.Sort();
int index = 0;
List<int> deletedIndex = new List<int>();
while (index < yourList.Count - 1)
{
    if (yourList[index] == yourList[index + 1])
    {
        yourList.RemoveAt(index);
        //index represents the position of deleted items
        deletedIndex.Add(index);
    }
    else
        index++;
}

// You can convert it back to an array if you would like to
int[] deletedIndexArray= deletedIndex.ToArray();

Posted 10-Dec-15 7:18am

ridoy

Updated 10-Dec-15 7:29am

v4

Comments

Matt T Heffron 10-Dec-15 13:25pm

Two points:
The question "smells" of being homework, so giving a complete solution is not doing the OP any long term benefit.
OP said the duplicate-free list needed to be a new list. (Presumably, so the deleted index values still correlate to something.)

ridoy 10-Dec-15 13:27pm

@Matt, answer is already updated, cheers!

Palash Sachan 10-Dec-15 13:47pm

this is it..this is what i wanted..thanks @ridoy

ridoy 10-Dec-15 14:39pm

Glad that helps you, i haven't tested the code, even don't write code in C# for long time. I just try to show you a way logically, nice to see that works for you, though someone voted a 1 for it, cheers!

Matt T Heffron 10-Dec-15 14:50pm

This doesn't preserve the original word order, and it is O(n²).
Still the OP says it is what is wanted, so ...

Solution 1

You can use Distinct to remove duplicate, see following code

C#

List<string> st = new List<string> { "Hello", "World", "Welcome", "To", "Csharp", "Welcome", "World", "Hello", "To", "Hello" }; //Example string array
           List<string> lst = st.Distinct().ToList();

Posted 10-Dec-15 7:07am

Anisuzzaman Sumon

Updated 10-Dec-15 7:08am

v2

Comments

Matt T Heffron 10-Dec-15 13:11pm

This doesn't give a separate array of the positions of the deleted strings, as required.

ridoy 10-Dec-15 13:35pm

@Sumon, its not what Matt wanted, its what OP wants: "also i want the positions of the deleted items in new array"

Palash Sachan 10-Dec-15 13:44pm

nice trick..thanks @Anisuzzaman Sumon for the quick answer :)

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Matt T Heffron · Accepted Answer · 2015-12-10T08:28:00

This is similar to Solution 2 by ridoy, except it preserves the original word order generating a new list for duplicate free result.
It is also O(n) in time complexity. (Which isn't a big deal unless st gets long!)

C#

List<string> st = new List<string> { "Hello", "World", "Welcome", "To", "Csharp", "Welcome", "World", "Hello", "To", "Hello" }; //Example string array
HashSet<string> seen = new HashSet<string>();
List<string> duplicateFree = new List<string>();
List<int> deletedIndices = new List<int>();
int ix = 0;
foreach (var s in st)
{
  // seen.Add(s) returns false if s is already in seen
  // so false means this s is a duplicate
  if (seen.Add(s))
  {
    duplicateFree.Add(s);
  }
  else
  {
    deletedIndices.Add(ix);
  }
  ++ix;
}
// duplicateFree is the cleaned-up list:
// { "Hello", "World", "Welcome", "To", "Csharp" }
// If really necessary to be an array:
int[] deletedIndicesArray = deletedIndices.ToArray();