从dart列表中提取常见元素 [英] extract common elements from lists in dart

问题描述

我有3个列表，例如:

  List l1 = [1, 2, 3, 55, 7, 99, 21];
  List l2 = [1, 4, 7, 65, 99, 20, 21];
  List l3 = [0, 2, 6, 7, 21, 99, 26];

我希望有共同的要素:

// [7,99,21]

这是我尝试过但无法正常工作的内容:

here is what i've tried but didn't work correctly:

 List l1 = [1, 2, 3, 55, 7, 99, 21];
 List l2 = [1, 4, 7, 65, 99, 20, 21];
 List l3 = [0, 2, 6, 7, 21, 99, 26];
 List common = l1;

 l2.forEach((element) {
   l3.forEach((element2) {
    if (!common.contains(element) || !common.contains(element2)) {
    common.remove(element);
    common.remove(element2);
    }
   });
 });

print(common);

另外，列表的数量是动态的，所以我希望像这样嵌套它们，我没有递归的经验，所以我做不到，甚至不知道它是否比嵌套循环好.

plus, the number of lists is dynamic, so i expect to nest them like this, i have no experience with recursion so i couldn't do it or even know if it's better than nesting loops.

感谢您的帮助.

推荐答案

一种解决方案:

void main() {
  List l1 = [1, 2, 3, 55, 7, 99, 21];
  List l2 = [1, 4, 7, 65, 99, 20, 21];
  List l3 = [0, 2, 6, 7, 21, 99, 26];

  l1.removeWhere((item) => !l2.contains(item));
  l1.removeWhere((item) => !l3.contains(item));

  print(l1);
}

结果:

[7，99，21]

[7, 99, 21]

如果列表的数量是动态的，那么一种解决方案是对所有列表中的所有出现次数进行计数，并且仅保留出现次数等于列表数量的值:

If your number of lists is dynamic, then a solution is to count all occurences within all the lists, and retains only values where number of occurence is equals to the number of lists :

void main() {
  List<List> lists = [
    [1, 2, 3, 55, 7, 99, 21],
    [1, 4, 7, 65, 99, 20, 21],
    [0, 2, 6, 7, 21, 99, 26]
  ];

  Map map = Map();
  for (List l in lists) {
    l.forEach((item) => map[item] = map.containsKey(item) ? (map[item] + 1) : 1);
  }

  var commonValues = map.keys.where((key) => map[key] == lists.length);

  print(commonValues);
}

结果:

(7，99，21)

(7, 99, 21)

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