Finding every nth element in a list in dart-CodePudding

I have a list of lists

List<List<double>> data = [[1,2,3],[1,2,3], [2,2,3], [2,2,3], [1,2,3],  ...];

I need to put the first element in the inner arrays in an array;

so result will be

<List<double> newData  = [1,1,2,2,1.....]

CodePudding user response：

If you want just the first element for each inner list, or you want one element in particular, try this.

  final data = [
    [1, 2, 3],
    [4, 5, 6]
  ];

  final newData = [...data.map((e) => e.first)];  // or elementAt(...)
  print(newData); // [1, 4]

If you want every element in that array (column-like), then I'll just try and brute force as follows (I'm sure there are better ways to do this with package:collection, but I'm unsure how atm).

import 'package:collection/collection.dart';

  const columnsAmount = 3;
  final data = [
    [1, 2, 3],
    [4, 5, 6]
  ];

  final result = <int, List<int>>{
    for (var i = 0; i < columnsAmount; i  ) i: []
  };
  for (final d in data) {
    d.forEachIndexed((index, element) {
      result[index]?.add(element);
    });
  }

  print(result);  // {0: [1, 4], 1: [2, 5], 2: [3, 6]}