What is the most efficient method to remove null values within an array.

Question

I am curious what the most efficient method of removing null values in arrays is. Here is my current null(0) removal method.

public static int[] removeNull(int[] array){
        int j = 0;
        for( int i=0;  i<array.length;  i++ )
        {
            if (array[i] != 0)
                array[j++] = array[i];
        }
        int [] newArray = new int[j];
        System.arraycopy( array, 0, newArray, 0, j );
        return newArray;
}

What is this method performance? I was expecting it to be n.

check this out :stackoverflow.com/questions/4150233/…

soorapadman
– soorapadman

2017-12-21 06:31:35 +00:00
Commented Dec 21, 2017 at 6:31 — soorapadman
– soorapadman, Commented Dec 21, 2017 at 6:31

Eran · Accepted Answer · 2017-12-21 07:06:57Z

5

Yes, your method's time complexity is O(n) - your loop has n (the length of the array) iterations, and copying an array requires time proportional to the size of the copied array, which in this case is O(n) in the worst case.

And you can't do better than that (in terms of time complexity), since you have to iterate over the entire array in order to locate the elements that should be removed.

If your goal is to reduce code complexity (i.e. write the shortest amount of code), you can use an IntStream (requires Java 8 or later):

public static int[] removeNull(int[] array) {
    return Arrays.stream(array).filter(i -> i != 0).toArray();
}

As Andreas commented, this solution has the advantage of leaving the original array unchanged.

edited Dec 21, 2017 at 7:06

answered Dec 21, 2017 at 6:29

Eran

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9 Comments

Andreas Over a year ago

Entirely agree. +1 However, code complexity can be improved by replacing last 3 lines with return Arrays.copyOf(array, j);

Eran Over a year ago

@joshLor yes, though 2n is asymptotically O(n).

Andreas Over a year ago

@Eran True, but I was sticking to plain non-stream Java, since so many on here are still pre-Java 8 Android users. --- One more +1 from me for adding stream solution. (Wish I could do another +1)

Eran Over a year ago

@joshLor 2n is the same thing as O(n) and 2n is also the same thing as O(n) - you got that right, twice :)

Andreas Over a year ago

Suggested clarification: Stream solution is for Java 8+, and has the advantage that it leaves original array unmodified.

|

Shreya Prajapati · Accepted Answer · 2017-12-21 07:01:58Z

0

Use filter method,

import java.util.Arrays;
import java.util.stream.Collectors;

public class RemoveNullValue {
    public static void main( String args[] ) {
        String[] firstArray = {"test1", "", "test2", "test4", "", null};

        firstArray = Arrays.stream(firstArray)
                     .filter(s -> (s != null && s.length() > 0))
                     .toArray(String[]::new);    

    }
}

edited Dec 21, 2017 at 7:01

answered Dec 21, 2017 at 6:29

Shreya Prajapati

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5 Comments

daniu Over a year ago

An int is not very probable to be null. In fact, I don't expect this to compile.

Shreya Prajapati Over a year ago

can check int with value of 0 and need to use Java 8

Andreas Over a year ago

Still won't make code compile, since input is an int[], not an ArrayList<Integer>

Shreya Prajapati Over a year ago

can use Arrays.stream(arrayList).filter() for int[] from link String[] firstArray = {"test1", "", "test2", "test4", "", null}; firstArray = Arrays.stream(firstArray) .filter(s -> (s != null && s.length() > 0)) .toArray(String[]::new);

Andreas Over a year ago

You should edit answer and fix it, rather than having (unformatted) code in a comment. Right now, answer is still wrong.

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