How to remove duplicate values in an array.

[m***@gmail.com]

I have some code to build an object elementData that stores a list of ints in an array and also keeps track of a boolean unique that determines if duplicates are allowed in a list. I have written a small method to search out duplicates and remove them, but for some reason it is not working. I am not sure if the problem is with the method itself or the placement of the call to the removeDuplicates method.

// post: places the value in the correct place based on ascending order
public void add(int value) {
size++;
if (size == 1) {
elementData[0] = value;
} else {
int position = Arrays.binarySearch(elementData, 0, size - 1, value);
if (position < 0 ) {
position = (-position) - 1;
}
for (int i = size - 1; i > position; i--) {
elementData[i] = elementData[i - 1];
}
elementData[position] = value;
if (unique) {
removeDuplicates();
}
}
}

//post: removes any duplicate values from the list
private void removeDuplicates() {
for(int i = size - 1; i < 0; i--) {
if (elementData[i] == elementData[i - 1]){
remove(i);
}
}
}
// pre : 0 <= index < size() (throws IndexOutOfBoundsException if not)
// post: removes value at the given index, shifting subsequent values left
public void remove(int index) {
checkIndex(index);
for (int i = index; i < size - 1; i++) {
elementData[i] = elementData[i + 1];
}
size--;
}

[Steven Simpson]

Post by m***@gmail.com
I have some code to build an object elementData that stores a list of ints in an array and also keeps track of a boolean unique that determines if duplicates are allowed in a list. I have written a small method to search out duplicates and remove them, but for some reason it is not working. I am not sure if the problem is with the method itself or the placement of the call to the removeDuplicates method.
// post: places the value in the correct place based on ascending order
public void add(int value) {
size++;
if (size == 1) {
elementData[0] = value;

(I'm not sure you need this branch. binarySearch would have to quickly
yield -1, position would take the value 0, the shifting loop would have
zero iterations, and the value would be assigned to position zero.)

Post by m***@gmail.com
} else {
int position = Arrays.binarySearch(elementData, 0, size - 1, value);
if (position < 0 ) {
position = (-position) - 1;
}
for (int i = size - 1; i > position; i--) {
elementData[i] = elementData[i - 1];
}
elementData[position] = value;
if (unique) {
removeDuplicates();
}

You're evidently relying on the sequence being sorted, and ensuring it
too - so your removeDuplicates could be limited to looking for them only
where the insertion just took place. Better still, detect a
non-negative from binarySearch, and don't bother inserting.

Post by m***@gmail.com
}
}
//post: removes any duplicate values from the list
private void removeDuplicates() {
for(int i = size - 1; i < 0; i--) {

Surely, i > 0?

Post by m***@gmail.com
if (elementData[i] == elementData[i - 1]){
remove(i);
}
}
}
// pre : 0 <= index < size() (throws IndexOutOfBoundsException if not)
// post: removes value at the given index, shifting subsequent values left
public void remove(int index) {
checkIndex(index);
for (int i = index; i < size - 1; i++) {
elementData[i] = elementData[i + 1];
}
size--;
}

Do you need the result to be sorted, or are you just using that to help
remove duplicates? If it's incidental, you could just add values to a
HashSet<Integer>.

If sorting is important, but you want to keep duplicates, you could use
a TreeMap:

SortedMap<Integer, Integer> map = new TreeMap<>();

void add(int value) {
Integer count = map.get(value);
if (count == null) count = 0;
count++;
map.put(value, count);
}

To sort but avoid duplicates:

SortedSet<Integer> set = Collections.newSetFromMap(new TreeMap<Integer, Boolean>());

void add(int value) {
set.add(value);
}

Or use unsorted collections, and sort after.

[Joerg Meier]

Post by m***@gmail.com
I have some code to build an object elementData that stores a list of ints in an array and also keeps track of a boolean unique that determines if duplicates are allowed in a list. I have written a small method to search out duplicates and remove them, but for some reason it is not working. I am not sure if the problem is with the method itself or the placement of the call to the removeDuplicates method.

If this isn't homework, I would recommend looking at the Java Collection
classes, many of which already allow you to filter for duplicates.

Liebe Gruesse,
Joerg

[Roedy Green]

I have some code to build an object elementData that stores a list of ints =
in an array and also keeps track of a boolean unique that determines if dup=
licates are allowed in a list. I have written a small method to search out =
duplicates and remove them, but for some reason it is not working. I am not=
sure if the problem is with the method itself or the placement of the call=
to the removeDuplicates method.

The lazy way to do this is it use an ArrayList which has a method for
removing.

[Lew]

Post by Roedy Green

I have some code to build an object elementData that stores a list of ints =
in an array and also keeps track of a boolean unique that determines if dup=
licates are allowed in a list. I have written a small method to search out =
duplicates and remove them, but for some reason it is not working. I am not=
sure if the problem is with the method itself or the placement of the call=
to the removeDuplicates method.

The lazy way to do this is it use an ArrayList which has a method for
removing.

Even lazier is to insert them into a Set.

--
Lew