Delete element from array

Question

Possible Duplicate:
Removing an element from an Array (Java)

Is there a way I can get rid of some elements in an array. for instance, if i have this array

int testArray[] = {0,2,0,3,0,4,5,6}

Is there a "fast" way to get rid of the elements that equal 0

int resultArray[] = {2,3,4,5,6}

I tried this function but I got lost using Lists

public int[] getRidOfZero(int []s){
   List<> result=new ArrayList<>();
   for(int i=0; i<s.length; i++){
     if(s[i]<0){
       int temp = s[i];
       result.add(temp);
     }
   }
   return result.toArray(new int[]);
}

Because this question specifically asks about removing elements in the middle of an array, it is really not the same thing - voting to reopen. — Yishai, Feb 23 '11 at 23:32

Matt Ball · Answer 1 · 2011-02-23T23:37:43.410

1

You're quite close, but:

Your generics were messed up (List<> is syntactically invalid)
Your comparison was only adding the element if it was less than zero (rather than adding it if it was not equal to zero)
~~You were calling the wrong toArray() method.~~Because ints are primitives, you have to turn the list back into an array yourself.

public int[] getRidOfZero(int[] s) {
    List<Integer> result = new ArrayList<Integer> ();
    for (int i : s) {
        if (i != 0) {
            result.add(i);
        }
    }

    int[] toReturn = new int[result.size()];
    for (int i=0; i<result.size(); i++) {
        toReturn[i] = result.get(i);
    }

    return toReturn;
}

edited Feb 23 '11 at 23:37

answered Feb 23 '11 at 23:21

Matt Ball

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Im guessing here temp would have to be an Integer object – Julio Diaz Feb 23 '11 at 23:25
@Julio: sorry, that's a typo on my part. Fixed. – Matt Ball Feb 23 '11 at 23:25
toArray returns an Object[] array, your method returns int[]. Primitives make this more painful. – Yishai Feb 23 '11 at 23:27
1

@Julio - no, neither `temp` nor `i` need to be an `Integer` object, thanks to the magic of Java [autoboxing](http://download.oracle.com/javase/1.5.0/docs/guide/language/autoboxing.html). – Mac Feb 23 '11 at 23:29
@Yishai: ngh... you're right. Fixed. – Matt Ball Feb 23 '11 at 23:35

score 1 · Accepted Answer · answered Feb 23 '11 at 23:22

Java arrays can't be resized. You need to create a new array.

Count the non-zero elements in the array. Create a new array that size. Copy the elements from the old to the new array, skipping over zero elements.

You can do this with lists. Your best bet is to create a list of Integers; add non-zero elements to it; then use toArray to create an array from the list.

score 0 · Answer 3 · answered Feb 23 '11 at 23:28

Since you're starting with an array, you'll need to create a new array and copy the items from the old array, excluding the zeros.

If you remove a bunch of zeros at once, this is going to be fast.

Otherwise, you'll need to begin with the doubly-linked LinkedList.

LinkedList has an iterator that allows you to move along the list and remove elements, which will be a constant-time operation.

Delete element from array

3 Answers3

Linked