Remove duplicates in arraylist

[Rajendra Prakash]

Correct this code to remove duplicates in arraylist1

import java.util.*;

class ArrayListRemoveDuplicates
{
	public static void main(String args[])
	{
		ArrayList<String> al1=new ArrayList<String>();
		al1.add("raja");
		al1.add("raja");
		al1.add("tendulkar");
		al1.add("prakash");
		al1.add("sachin");
		al1.add("sachin");	
		al1.add("zaheer");		
		al1.add("asin");
		al1.add("surya");
		for(String str1:al1)
		{
			System.out.println(str1);
		}
		ArrayList<String> al2 = new ArrayList<String>();
		for(String str2:al1)
		{
			if(!al2.equals(al1))		
			{
				al2.add(str2);
				
			}
		
		}
		System.out.println(al2);
	}
}		

[N.Senthil Kumar]

Hi Raj,

Why don't you use Set instead of List, if you don't need duplicates

[Christophe Verré]

Correct this code to remove duplicates in arraylist1

The ranch is NotACodeMill. If you have some difficulties, tell us where you find yourself stuck at. What did you try ?

And there isn't any arraylist1 in your code...

[Sunil Tiwari]

Try this! This is a very trivial solution!

    

import java.util.*;

public class ArrayListRemoveDuplicates
{
	public static void main(String args[])
	{
		ArrayList<String> al1=new ArrayList<String>();
		al1.add("raja");
		al1.add("raja");
		al1.add("tendulkar");
		al1.add("prakash");
		al1.add("sachin");
		al1.add("sachin");	
		al1.add("zaheer");		
		al1.add("asin");
		al1.add("surya");

		Set<String> set = new HashSet<String>();
		set.addAll(al1);
		
		System.out.println("Arraylist " + al1);
		System.out.println("Set       " + set);
	}
}		


Output : 
Arraylist [asin, prakash, raja, raja, sachin, sachin, surya, tendulkar, zaheer]
Set       [surya, zaheer, sachin, asin, tendulkar, raja, prakash]

[Rajendra Prakash]

ok , can you give atleast logic to remove duplicates in arraylist without hashset.

[Christophe Verré]

if(!al2.equals(al1)) 

What are you checking here ? Shouldn't you check if str2 is not already in in al2 ?

[Sunil Tiwari]

Another trivial solution

    
import java.util.*;

public class ArrayListRemoveDuplicates
{
	public static void main(String args[])
	{
		ArrayList<String> al1=new ArrayList<String>();
		al1.add("raja");
		al1.add("raja");
		al1.add("tendulkar");
		al1.add("prakash");
		al1.add("sachin");
		al1.add("sachin");	
		al1.add("zaheer");		
		al1.add("asin");
		al1.add("surya");

		/*Set<String> set = new HashSet<String>();
		set.addAll(al1);*/
		
		ArrayList<String> al2=new ArrayList<String>();
		
                for (PossibleAnswer answer : answers) {
                    post.remove(answer);
		}
		
		System.out.println("Arraylist al1 " + al1);
		System.out.println("Arraylist al2 " + al2);
		//System.out.println("Set       " + set);
	}
}		


Output:
Arraylist al1 [raja, raja, tendulkar, prakash, sachin, sachin, zaheer, asin, surya]
Arraylist al2 [raja, tendulkar, prakash, sachin, zaheer, asin, surya]

[David Newton]

Please do not provide outright answers, rather give hints, suggestions, etc. as to how to solve the problem. Learning is more effective this way. Thanks!

[Sunil Tiwari]

Sure David!

[Ronald de Gier]

You really had me searching for an answers variable...

The java collection tutorials show some tricks to remove duplicates.

And how iterators work and such, for when you need to show you can manually remove duplicates.

[Rajendra Prakash]

can you correct 2 Errors in the following code
1.what parameter should be passed in RemoveDuplicates().
2.Incompatible types : return ret

import java.util.*;

class Raja
{
	public String RemoveDuplicates(ArrayList list) 	
	{
		boolean bl=false;
		ArrayList<String> ret=new ArrayList<String>();
		ret.add("raja");
		ret.add("asin");
		ret.add("sachin");
		ret.add("prakash");
		
		for(String str:ret) 
		{
			if(!ret.contains(str))
				 ret.add(str);
		}
		return ret;
	}
}
class RemoveDuplicatesInArrayList
{
	public static void main(String args[])
	{
		Raja r=new Raja();
		r.RemoveDuplicates();
	}
}

[Ronald de Gier]

Rajendra Prakash wrote: can you correct 2 Errors in the following code
1.what parameter should be passed in RemoveDuplicates().
2.Incompatible types : return ret

What are you using parameter list for? It doesn't seem to be used in the function.

What are your thoughts on the code so far?

[Rajendra Prakash]

I passed list object in the RemoveDuplicate(), but compiler error.
return statement also throws compiler error

[David Newton]

Well, you're not returning the type you say you are. And you're checking every item in the list you just created against the list you just created, so every element is pretty much guaranteed to be in the list... because you put it there. And if it's not there (impossible), you put it back into the same list.

I suspect what you meant to do was check every item in the list you pass in (which you don't do) against the return list--maybe head down that road and post a followup with your new code.

[Sean Clark]

Hey,

Can I suggest that you check if the element is in the list before you add it? Collections have a contains method which returns a boolean as to whether an element exists. Can I suggest you use the contains method to decide whether or not an item is already in the list and thus whether or not you have to add the item..

Edit: Doh missed the above post, sorry guys.

Sean

[Mukesh Ranjan]

It is almost a bad idea to remove duplicate and using loops for that.

Its better to use hashset then, below is the example code;

ArrayList<String> al1 = new ArrayList<String>();
al1.add("raja");
al1.add("raja");
al1.add("tendulkar");
al1.add("prakash");
al1.add("sachin");
al1.add("sachin");
al1.add("zaheer");
al1.add("asin");
al1.add("surya");

HashSet<String> set = new HashSet<String>(al1);

Iterator iterator = set.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}

Answer:
asin
prakash
tendulkar
surya
sachin
zaheer
raja

[David Newton]

David Newton wrote:Please do not provide outright answers, rather give hints, suggestions, etc. as to how to solve the problem. Learning is more effective this way. Thanks!

And when you *do* violate the spirit of JavaRanch, at least UseCodeTags.

[Mukesh Ranjan]

Agreed !!

[Vigneshwar Subramanian]

Rajendra Prakash wrote:Correct this code to remove duplicates in arraylist1

import java.util.*;

class ArrayListRemoveDuplicates
{
	public static void main(String args[])
	{
		ArrayList<String> al1=new ArrayList<String>();
		al1.add("raja");
		al1.add("raja");
		al1.add("tendulkar");
		al1.add("prakash");
		al1.add("sachin");
		al1.add("sachin");	
		al1.add("zaheer");		
		al1.add("asin");
		al1.add("surya");
		for(String str1:al1)
		{
			System.out.println(str1);
		}
		ArrayList<String> al2 = new ArrayList<String>();
		for(String str2:al1)
		{
			if(!al2.equals(al1))		
			{
				al2.add(str2);
				
			}
		
		}
		System.out.println(al2);
	}
}		

After printing 'al2' we get a list with duplicates .... wat will be the problem i detected tat problem is with if(!al2.equals(al1)) statement but i could not recognize wats d problem .. if v remove
the not symbol '!' then the control isn't not coming inside the for loop itself

[Ishan Pandya]

@vigneshwar- dude have you hear of bubble sort algorithm? it checks the first value with each an every value of array/list.
try doing with that and post what happens.

[Ishan Pandya]

@OP - why do you compulsory need to use List for unique elements? is there any specific requirement for that?

[Winston Gutkowski]

Ishan Pandya wrote:@OP - why do you compulsory need to use List for unique elements? is there any specific requirement for that?

I think OP is long gone. Look at the date of his post.

Winston

[Ishan Pandya]

Winston Gutkowski wrote:
I think OP is long gone. Look at the date of his post.

yes actually. he must have found out something for sure.