Define "remove".
Arrays are fixed length and can not be resized once created. You can set an element to null to remove an object reference;
for (int i = 0; i < myStringArray.length(); i++)
{
if (myStringArray[i].equals(stringToRemove))
{
myStringArray[i] = null;
break;
}
}
or
myStringArray[indexOfStringToRemove] = null;
If you want a dynamically sized array where the object is actually removed and the list (array) size is adjusted accordingly, use an ArrayList<String>
myArrayList.remove(stringToRemove);
or
myArrayList.remove(indexOfStringToRemove);
Edit in response to OP's edit to his question and comment below
String r = myArrayList.get(rgenerator.nextInt(myArrayList.size()));
Answer from Brian Roach on Stack OverflowDefine "remove".
Arrays are fixed length and can not be resized once created. You can set an element to null to remove an object reference;
for (int i = 0; i < myStringArray.length(); i++)
{
if (myStringArray[i].equals(stringToRemove))
{
myStringArray[i] = null;
break;
}
}
or
myStringArray[indexOfStringToRemove] = null;
If you want a dynamically sized array where the object is actually removed and the list (array) size is adjusted accordingly, use an ArrayList<String>
myArrayList.remove(stringToRemove);
or
myArrayList.remove(indexOfStringToRemove);
Edit in response to OP's edit to his question and comment below
String r = myArrayList.get(rgenerator.nextInt(myArrayList.size()));
It is not possible in on step or you need to keep the reference to the array. If you can change the reference this can help:
String[] n = new String[]{"google","microsoft","apple"};
final List<String> list = new ArrayList<String>();
Collections.addAll(list, n);
list.remove("apple");
n = list.toArray(new String[list.size()]);
I not recommend the following but if you worry about performance:
String[] n = new String[]{"google","microsoft","apple"};
final String[] n2 = new String[2];
System.arraycopy(n, 0, n2, 0, n2.length);
for (int i = 0, j = 0; i < n.length; i++)
{
if (!n[i].equals("apple"))
{
n2[j] = n[i];
j++;
}
}
I not recommend it because the code is a lot more difficult to read and maintain.
Videos
I would do it as follows:
String[] str_array = {"item1","item2","item3"};
List<String> list = new ArrayList<String>(Arrays.asList(str_array));
list.remove("item2");
str_array = list.toArray(new String[0]);
If you must use arrays, System.arraycopy is the most efficient, scalable solution. However, if you must remove one element from an array several times, you should use an implementation of List rather than an array.
The following utilizes System.arraycopy in order to achieve the desired effect.
public static Object[] remove(Object[] array, Object element) {
if (array.length > 0) {
int index = -1;
for (int i = 0; i < array.length; i++) {
if (array[i].equals(element)) {
index = i;
break;
}
}
if (index >= 0) {
Object[] copy = (Object[]) Array.newInstance(array.getClass()
.getComponentType(), array.length - 1);
if (copy.length > 0) {
System.arraycopy(array, 0, copy, 0, index);
System.arraycopy(array, index + 1, copy, index, copy.length - index);
}
return copy;
}
}
return array;
}
Also, you can increase the method's efficiency if you know that your array consists of only Comparable objects. You can use Arrays.sort to sort them before passing them through the remove method, modified to use Arrays.binarySearch to find index rather than a for loop, raising that portion of the method's efficiency from O(n) to O(nlogn).
You need 2 indices in the second loop, since you are iterating over two arrays (the input array and the output array) having different lengths.
Besides, newLength is a confusing name, since it doesn't contain the new length. It contains the difference between the input array length and the output array length. You can change its value to match its name.
int newLength = arr.length;
for(int i = 0; i < arr.length; i++)
{
if(arr[i].contains(toRemove))
{
newLength--;
}
}
String[] result = new String[newLength];
int count = 0; // count tracks the current index of the output array
for(int i = 0; i < arr.length; i++) // i tracks the current index of the input array
{
if(!arr[i].contains(toRemove)) {
result[count] = arr[i];
count++;
}
}
return result;
There's the error that @Eran pointed out in your code, which can solve your problem. But I'm going to discuss another approach.
For now, you're first iterating over the entire array to find the number of occurrences to remove, and then, you're iterating over the array to remove them. Why don't you just iterate over the array, just to remove them. (I know, your first loop is helping you to determine the size of the output array, but you don't need that if you use some List like ArrayList etc.)
List<String> resultList = new ArrayList<String>();
for(int i = 0; i < arr.length; i++)
{
if(!arr[i].contains(toRemove))
{
resultList.add(arr[i]);
}
}
And you can return the resultList, but if you really need to return an array, you can convert the resultList to an array like this:
String [] resultArray = resultList.toArray(new String[resultList.size()]);
And then return this array. See this approach live here on ideone.
You could use commons lang's ArrayUtils.
array = ArrayUtils.removeElement(array, element)
commons.apache.org library:Javadocs
Your question isn't very clear. From your own answer, I can tell better what you are trying to do:
public static String[] removeElements(String[] input, String deleteMe) {
List result = new LinkedList();
for(String item : input)
if(!deleteMe.equals(item))
result.add(item);
return result.toArray(input);
}
NB: This is untested. Error checking is left as an exercise to the reader (I'd throw IllegalArgumentException if either input or deleteMe is null; an empty list on null list input doesn't make sense. Removing null Strings from the array might make sense, but I'll leave that as an exercise too; currently, it will throw an NPE when it tries to call equals on deleteMe if deleteMe is null.)
Choices I made here:
I used a LinkedList. Iteration should be just as fast, and you avoid any resizes, or allocating too big of a list if you end up deleting lots of elements. You could use an ArrayList, and set the initial size to the length of input. It likely wouldn't make much of a difference.
its better to use arraylist
arr_fav = {"1","2","3"};
List<String> numlist = new ArrayList<String>();
for(int i= 0;i<arr_fav.length;i++)
{
if(current_id == Integer.parseInt(arr_fav[i]))
{
// No operation here
}
else
{
numlist.add(arr_fav[i]);
}
}
arr_fav = numlist .toArray(new String[numlist .size()]);
You don't.
Arrays can not be resized.
You would need to create a new (smaller) array, and copy the elements you wished to preserve into it.
A better Idea would be to use a List implementation that was dynamic. An ArrayList<Integer> for example.
So guys i'm having trouble finding a solution for this question. I'm kinda frustrated that i didn't solve this kind of problem during my exam for employment.
Problem: The task is to provide an implementation for the given function. int[] removeElem(int[] array, value), the objective is to find if the array contains the given 'value' inside it. if found then remove the element from the array then return an array with a new size, else return original array.
So far this is what i got:
public static void main(String[] args) {
int[] myArray = {5,6,9,4};
int[] newArray = removeElem(myArray,9);
for(int i=0;i<newArray.length;i++){
System.out.print(newArray[i] + " ");
}
}
public static int[] removeElem(int[] array, int value){
int[] tempArray = array;
int newArrayLength = 0;
int[] newArray;
for(int index=0;index < tempArray.length; index++){
if(tempArray[index] == value){
tempArray[index] = -1;
newArrayLength++;
}
}
newArray = new int[tempArray.length - newArrayLength];
for(int index=0;index < newArray.length; index++){
if(tempArray[index] != -1){
newArray[index] = tempArray[index];
}
}
return newArray;
}Unfortunately i can't get it right :/
Edit: Thank you! everyone for suggesting different solutions to this problem, I feel like I need to work more on my solutions and such :|.
If example is not final then a simple reassignment would work:
example = new String[example.length];
This assumes you need the array to remain the same size. If that's not necessary then create an empty array:
example = new String[0];
If it is final then you could null out all the elements:
Arrays.fill( example, null );
- See: void Arrays#fill(Object[], Object)
- Consider using an
ArrayListor similar collection
example = new String[example.length];
If you need dynamic collection, you should consider using one of java.util.Collection implementations that fits your problem. E.g. java.util.List.