chunked_list.dart

import 'dart:math';

extension ChunkedList<T> on List<T> {
  /// Slice this list in chunks of a given [size].
  ///
  /// If [size] is a negative number it will slice the reverse list of [this].
  ///
  /// Set [incomplete] to `true` in order to include an incomplete chunk (if any).
  ///
  /// Usage:
  /// ```dart
  /// print(<int>[1, 2, 3, 4, 5].chunked(2, incomplete: false)); // [[1, 2], [3, 4]]
  /// print(<int>[1, 2, 3, 4, 5].chunked(2, incomplete: true)); // [[1, 2], [3, 4], [5]]
  /// print(<int>[1, 2, 3, 4, 5].chunked(-2, incomplete: false)); // [[5, 4], [3, 2]]
  /// print(<int>[1, 2, 3, 4, 5].chunked(-2, incomplete: true)); // [[5, 4], [3, 2], [1]]
  /// ```
  ///
  /// Throws an [ArgumentError] if [size] is zero.
  List<List<T>> chunked(int size, {bool incomplete = false}) {
    if (size == 0) {
      throw ArgumentError.value(
        size,
        'chunked',
        '[size] must be a non-zero integer.',
      );
    }

    final List<T> target = size.isNegative ? reversed.toList() : toList();

    final int n = size.abs();

    final int base = incomplete ? (length / n).ceil() : (length / n).floor();

    return <List<T>>[
      for (int i = 0; i < base; i++)
        target.sublist(i * n, min((i + 1) * n, length)),
    ];
  }
}

void main() {
  print(<int>[1, 2, 3, 4, 5].chunked(2, includeIncomplete: false));  // [[1, 2], [3, 4]]
  print(<int>[1, 2, 3, 4, 5].chunked(2, includeIncomplete: true));   // [[1, 2], [3, 4], [5]]
  print(<int>[1, 2, 3, 4, 5].chunked(-2, includeIncomplete: false)); // [[5, 4], [3, 2]]
  print(<int>[1, 2, 3, 4, 5].chunked(-2, includeIncomplete: true));  // [[5, 4], [3, 2], [1]]
}