使用ramda.js中的嵌套字段进行排序

Question

In the documentation of sortBy , it says we can use R.prop to sort an object by it's field. But if I have to sort by a nested field, it does not work. For example R.prop('id.number') does not work.

var items = [{id:3},{id:1},{id:2}];
var sorter = R.sortBy(R.prop('id'));
sorter(items)

works fine. But if I have a nested structure

var items = [{id:{number:3}},{id:{number:1}},{id:{number:2}}];
var sorter = R.sortBy(R.prop('id.number'));
sorter(items)

returns me an empty list. I guess there is a correct way of using R.prop that I am not able to figure out.

Answer 1

您可以使用R.path来访问嵌套属性，因此您的示例将成为R.sortBy(R.path(['id', 'number']))

Answer 2

Unless I'm mistaken, id.number itself is being checked as a property, when in fact there is only the property id . R.prop() only checks one level down - nested structures are beyond its ability, and being asked to look for the property number after doesn't work .

The documentation states that sortBy accepts a function which takes an element under consideration. The following is tested on the ramda.js REPL and works:

var items = [{id:{number:3}},{id:{number:1}},{id:{number:2}}];
var sorter = R.sortBy(function(item) {return item['id']['number'];});
sorter(items)

It works by simply looking up the properties in succession.

tl;dr Anonymous functions for the win.