30秒学会 Dart 片段 – zip

Creates a list of elements, grouped based on the position in the original lists.

Use List.generate() to generate a list, using Iterable.map(), Iterable.reduce() and max() to get the longest sublist.
Use List.generate() inside the iterator to generate the sublists, using the appropriate indexes to get their values from the original list.

代码实现

import 'dart:math';

List<List<T>> zip<T>(List<List<T>> itr) {
  return List.generate(
      itr.map((x) => x.length).reduce(max),
      (i) => List.generate(
          itr.length, (k) => itr[k].length > i ? itr[k][i] : null));
}

使用样例

zip([['a', 'b'], [1, 2], [true, false]]); // [['a', 1, true], ['b', 2, false]]
zip([['a'], [1, 2], [true, false]]); // [['a', 1, true], [null, 2, false]]