通过Immutable.js中的特定键对有序映射进行排序

Question

请检查这个小提琴示例

如何orderedMap通过键sequence按降序对对象进行排序？我知道有一种sortBy方法,但文件没有给出一个更清晰的例子.

这是我的原始对象:

var props = {
  "item": {
    "A": {
      "sequence": 5
    },
    "B": {
      "sequence": null
    },
    "C":{
      "sequence": 2
    }
  }
}

我希望结果如下:

var props = {
  "item": {
    "A": {
      "sequence": 5
    },
    "C":{
      "sequence": 2
    },
    "B": {
      "sequence": null
    }
  }
}

示例代码:

var data = Immutable.fromJS(props,(key, value)=>{
     var isIndexed = Immutable.Iterable.isIndexed(value);
     return isIndexed ? value.toList() :value.toOrderedMap();
});

var sorted = data.get('item').sortBy((item) => item.get('sequence'));

console.log(sorted.toJS())

Answer 1

您提供的功能sortBy()是比较器,它需要返回一个数字.通过在结果前面item.get('sequence')或后面添加一个减号,reverse()您将反转排序,获得您想要的输出.

这是一个例子:

var sorted = data.get('item').sortBy((item) => -item.get('sequence'));
// or var sorted = data.get('item').sortBy((item) => item.get('sequence')).reverse();
// you can now use .map() to go through your OrderedMap which has been
// sortbed by the sequence property and would look like your desired output

请注意,您正在使用OrderedMap,并且只是调用sorted.toJS()将返回一个常规JS对象,其中键显然没有排序.

// If you need to iterate through the map and return some 
// plain JS you can do something like:
sorted.map(x => x.get('sequence')).toJS()
// => Object {A: 5, C: 2, B: null}