Java如何从嵌套数组列表中删除项目

Question

I have a nested ArrayList as below with boolean values. I want to remove for example 3rd item from all the rows. I tried with a loop but it doesnt resolve remove as a method. How should I do this? Many thanks for your help.

for (int i = 0; i < list.size(); i++){
     list.get(i).remove(3)// this remove method shows as an error in IDE
 }

true    false   true    false   false   false
false   false   true    false   true    true

Answer 1

... It's a list of List<Instance> listInstances = new ArrayList<Instance>(); and the class Instance has vals = new ArrayList<Boolean>(); ....

In this case your solution can look like :

public static Instance deleleNthElement(Instance instance, int index) {
    instance.getVals().remove(index - 1);
    return instance;
}

then with stream you can call the method like so :

int index = 3;
listInstances = listInstances.stream()
          .map(instance -> deleleNthElement(instance, index))
          .collect(Collectors.toList());

Answer 2

I see no error in your logic, I believe you are missing a ';' from the end of the remove(3).
By the way, List is an Interface, you will need to instanciate as an ArrayList (or some such).

Answer 3

I strung the following together, seems to do what you intended:

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Test {

    public static void main(String[] args) throws IOException {

        List<Boolean> row1 = new ArrayList<Boolean>(Arrays.asList(new Boolean[] {true,false,true,true}));
        List<Boolean> row2 = new ArrayList<Boolean>(Arrays.asList(new Boolean[] {true,true,false,true}));
        List<List<Boolean>> list = Arrays.asList(new ArrayList[] {(ArrayList) row1, (ArrayList) row2});

        for (int i=0;i<list.size();i++){
            list.get(i).remove(3);// this remove method shows as an error in IDE
        }
        for (List<Boolean> ll : list) {
            for (Boolean l : ll) {
                System.out.print(l + ",");
            }
            System.out.println();
        }
    }
}