CODEWITHSUNDEEP
javaarrayslist
hollabaloo
hollabaloo

Reputation: 853

Comparing and removing elements not present in a List and array java

I have one String array and one List<String>. What I want to do is to use the variable with a larger size and use that as the basis of the values removal of the smaller variable. I also want to get the values of the larger sized variable not present in the other. Note that the reason why the two variables differ on datatype is because the String[] group variable is a checkbox group from a jsp page and the List<String> existingGroup is a ResultSet from the database. For example:

String[] group contains:

Apple
Banana
Juice
Beef

List<String> existingGroup contains:

Apple
Beef
Lasagna
Flower
Lychee

And since the size of the two variables vary, it should still correctly remove the values.

What I have so far is

    if(groupId.length >= existingGroup.size()) {
        for(int i = 0; i < groupId.length; i++) {
            if(! existingGroup.contains(groupId[i])) {
                if(existingGroup.get(existingGroup.indexOf(groupId[i])) != null) {
                    // I'm unsure if I'm doing this right
                }
            }
        }
    } else {
        for(int i = 0; i < existingGroup.size(); i++) {
            // ??
        }
    }

Thanks.

Upvotes: 2

Views: 4197

Answers (2)

Rahul
Rahul

Reputation: 45060

You can use the methods the List interface provides.

list.removeAll(Arrays.asList(array)); // Differences removed

or

list.retainAll(Arrays.asList(array)); // Same elements retained

based on your needs.

Upvotes: 3

Petr Mensik
Petr Mensik

Reputation: 27496

Ok, I would start with converting your array into the List too. So do

List<String> input = Arrays.asList(array);
//now you can do intersections
input.retainAll(existingGroup); //only common elements were left in input

Or, if you want elements which are not common, just do

existingGroup.removeAll(input); //only elements which were not in input left
input.removeAll(existingGroup); //only elements which were not in existingGroup left

Choice is yours:-)

Upvotes: 4

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