如何计算列表中项目的出现次数

问题描述：

我是 Dart 的新手.目前我有一个重复项目列表，我想计算它们的出现次数并将其存储在 Map 中.

I am new to Dart. Currently I have a List of duplicate items, and I would like to count the occurence of them and store it in a Map.

var elements = ["a", "b", "c", "d", "e", "a", "b", "c", "f", "g", "h", "h", "h", "e", "a"];

我希望得到如下结果:

{
  "a": 3,
  "b": 2,
  "c": 2,
  "d": 2,
  "e": 2,
  "f": 1,
  "g": 1,
  "h": 3
}

我做了一些研究并找到了一个 JavaScript 解决方案，但我不知道如何将其翻译成 Dart.

I did some research and found a JavaScript solution, but I don't know how to translate it to Dart.

var counts = {};
your_array.forEach(function(x) { counts[x] = (counts[x] || 0)+1; });

答

试试这个:

  var elements = ["a", "b", "c", "d", "e", "a", "b", "c", "f", "g", "h", "h", "h", "e"];
  var map = Map();

  elements.forEach((element) {
    if(!map.containsKey(element)) {
      map[element] = 1;
    } else {
      map[element] +=1;
    }
  });

  print(map);

它的作用是:

遍历列表元素
如果您的地图没有将列表元素设置为键，则创建值为 1 的该元素
否则，如果元素已经存在，则在现有的键值上加1

或者，如果你喜欢语法糖和一个衬垫，试试这个:

Or if you like syntactic sugar and one liners try this one:

  var elements = ["a", "b", "c", "d", "e", "a", "b", "c", "f", "g", "h", "h", "h", "e"];
  var map = Map();

  elements.forEach((x) => map[x] = !map.containsKey(x) ? (1) : (map[x] + 1));

  print(map);

在所有编程语言中有很多方法可以实现这一点！

There are many ways to achieve this in all programming languages!

如何计算列表中项目的出现次数

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