ArrayList

[stormswimmer]

Does anyone know how i could remove objects from an array list that are the same
ex:
1
2
4
4
4
5
changing array list values to
1
2
4
5
Thanx for any help

[noelob]

Hi,

ArrayList<Integer> duplicates = new ArrayList<Integer>()
Integer previous = new Integer(Integer.MIN_VALUE); // so it wont conflict with list values
for(int i=0; i<arrayList.size(); i++) // arrayList is your list
{
    // first find duplicates
    if(arrayList.get(i).equals(previous))
        duplicates.add(i);  // add the index of the duplicate

    else{
        previous = arrayList.get(i);
    }
}

// now remove duplicates
for(int j= duplicates.size()-1; j>=0; j--)
{
    arrayList.remove(duplicates.get(j));
}

Kind regards,
Noel

[nspils]

If you were wanting to create a collection of discrete values while not getting rid of your original list, you can create an instance of CopyOnWriteArraySet using the CopyOnWriteArraySet( ArrayList yourArrayList) constructor - then iterate through the list. Or copy the elements to a collection implementing the Set interface yourself ...

[stormswimmer]

That method isn't working
I am trying to calculate the mode I am using 2 methods

public static ArrayList duplicates(ArrayList modual)
    {
        Collections.sort(modual); 
        Double previous = (Double)modual.get(1); 
        ArrayList duplicate = new ArrayList();
        for(int i = 0; i < modual.size()-1; i++)
        {
            double temp = (Double) (modual.get(i)); 
            if(temp == previous)
            {
                duplicate.add(temp); 
            }
            else
            {
                previous = (Double) modual.get(i);
            }
        } 
        for(int j = 0; j <= duplicate.size()-1; j++)
        { 
            modual.remove(duplicate.get(j));   
        }
        return modual; 
    }

the purpose of this code is to take in the arraylist and remove the duplicates

    public static ArrayList mode(double array[]) throws IOException
    {
        double n;
        int freq = 0;
        int Mfreq = 0;
        double Mn = array[0];
        ArrayList modes = new ArrayList(); 
        PrintStream fout = new PrintStream( new FileOutputStream("output.txt"));
        for (int i = 0; i < array.length; i++) 
        {
            n = array[i];  
            if(i == 0 || array[i] != array[i - 1])
            { 
                for (int j = 0; j < array.length; j++) 
                {  
                    if (array[j] == n) 
                    { 
                        freq++;  
                    }
                }
            }
            if(freq != 0)
            {
                modes.add(freq+" "+array[i]);
            }
            freq = 0;
            if (freq > Mfreq) 
            {
                Mn = n;
            }
        }
        double mode = 0.0; 
        double oc = 0.0; 
        String str [] = new String [modes.size ()];
        modes.toArray (str);
        ArrayList modual = new ArrayList(); 
        for(int i = 0; i <= modes.size() -1; i ++)
        {
            
            String temp =  (String) (modes.get(i));
            int pos = str[i].indexOf(' ') ;
            String occ = str[i].substring(0 , pos); 
            int occurances = Integer.parseInt(occ); 
            occ = str[i].substring(pos, str[i].length()); 
            double number = Double.parseDouble(occ); 
            if(occurances >= oc)
            {
                modual.add(number);                
                oc = occurances; 
            }   
        }
        return modual; 
    }

the purpose of this method is to take in an array and caluclate the mode

[destin]

Does anyone know how i could remove objects from an array list that are the same
ex:
1
2
4
4
4
5
changing array list values to
1
2
4
5
Thanx for any help

The indexOf and lastIndexOf methods will work nicely.

public ArrayList removeDuplicates(ArrayList al) {
    for (int i = 0; i < al.size(); i++) {
        while (i != al.lastIndexOf(al.get(i))) {
            al.remove(al.lastIndexOf(i));
        }
    }
    return al;
}

That might be a bit sloppy to read... but basically, it loops through the ArrayList. At each index, it checks if that index equals the last index with the same object. If they are the same, there's only one in there. If they do not equal, it will remove all of the duplicates.

[stormswimmer]

This method doesn't work either i get a ArrayIndexOutOfBoundsException

[nspils]

public TreeSet<Integer> removeDuplicates (ArrayList<Integer> myArray)
{
     TreeSet<Integer> mySet = new TreeSet<Integer>();
      mySet.addAll( myArray );
      return mySet;
}

public void printSet( TreeSet<Integer> printSet )
{
     for ( Integer i : printSet )
     {
           System.out.print( i );
     }
     System.out.println();
}

[stormswimmer]

How does this method work?

[destin]

This method doesn't work either i get a ArrayIndexOutOfBoundsException

That's not because of my method. I just compiled and tested it; it works fine. Besides, nothing in the ArrayList class throws an ArrayIndexOutOfBoundsException; it does throw IndexOutOfBoundsExceptions though.