Removing Item From List by Index Causes Index to Change

Question

As I'm attempting to remove an item from a List by the items respective index value I'm realizing (in a "going nuts" sort of way), that again because of pass by referencing I'm getting unexpected results as a developer not used to that concept (learning to like it but not sure how to work around things like this).

Basically once I remove the first index value that then affects the list I'm removing items from so that the next index I want to remove is wrong. This continues perpetually causing the wrong items to be removed from my list.

List<Integer> null values = new List<>(0,2,4);
for(Integer i : nullValues){ 
    myList.remove(i);
}

What's the trick? How do I avoid this typically, at least in this small example here?

Answer 1

Try below,

List<Integer> nullvalues = new List<Integer>{0,2,4};
nullvalues.sort();//sorts in ascending order

//Iterate descending & remove one by one
for(Integer i=nullvalues.size()-1;i>=0;i--){     
    if(nullvalues[i]<myList.size()){
       myList.remove(nullvalues[i]);
    }
}

Dont forget to accepts answer if its helpful. Tia

Answer 2

Try removing values from the end of the list first:

Integer sz = myList.size() - 1;
for (Integer i = sz; i >= 0; i--) {
    myList.remove(i);
}

Answer 3

If I understand correctly you want to remove items from the List of myList that has the same index's as the null value list?

Is this a list of sObjects? If so use the List deepClone method to clone null values into the my list.

That way it will not be a shallow copy (by reference).

So

sObject[] myList = nullValues.deepClone(true);

for(integer x=0;x<nullvalues.size();x++){
    myList.remove(x);
}

Now the problem will be that once you remove the values from myList the index's will change so you will need to keep a count of that so you can reference it

So it becomes

Integer offset = 0;

sObject[] myList = nullValues.deepClone(true);

for(integer x=0;x<nullvalues.size();x++){
    myList.remove(x-offset);
    offset++;
}

When it is over, nullValues will be unchanged....

This assumes I understood your question correctly. If I did not please clarify your question with additional code, what you expect to happen, etc...