How to make nested lists work properly in dart?

Question

I'm trying to create nested Lists but the output I got is not what I have expected.

void main() {
  List<int> row = List();
  List<List<int>> rows = List();

  for(int i=0;i<5;i++)
  {

    row.add(i+1);
    row.add(i+2);
    row.add(i+3);
    rows.add(row);
    row.clear();
  }

  print(rows);
}

The output I got :

[[], [], [], [], []]

The output I was Expecting:

[[1,2,3],[2,3,4],[3,4,5],[4,5,6],[5,6,7]]

What changes can I should make run this code properly?

On each iteration, you add a reference to the same List instance (row). Since you ultimately clear that instance, you end up with a List of empty Lists. You want to add separate List instances instead (e.g. rows.add([...row]) or rows.add(List<int>.of(row)).) — jamesdlin
– jamesdlin, Commented May 20, 2020 at 19:12

EdwynZN · Accepted Answer · 2020-05-20 19:27:02Z

2

As @shubham answer says, you should create the List inside the for loop because you're referencing the same object, so when you're clearing at the end of the for that also cleanse all the objects inside

answered May 20, 2020 at 19:27

EdwynZN

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Comments

Shubham Gupta · Accepted Answer · 2020-05-20 19:16:34Z

1

This should help you.

void main() {
  List<List<int>> rows = List();

  for (int i = 0; i < 5; i++) {
    List<int> row = List();
    row.add(i + 1);
    row.add(i + 2);
    row.add(i + 3);
    rows.add(row);
  }
  print(rows); 
}

answered May 20, 2020 at 19:16

Shubham Gupta

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Comments

Aidan Ahram · Accepted Answer · 2024-02-05 23:34:41Z

0

I think the @Shubham's code is outdated. Try using this:

void main() {
  List<List<int>> rows = [];

  for (int i = 0; i < 5; i++) {
    List<int> row = [];
    row.add(i + 1);
    row.add(i + 2);
    row.add(i + 3);
    rows.add(row);
  }
  print(rows); 
}

answered Feb 5, 2024 at 23:34

Aidan Ahram

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