如何在Jsonata中基于两个值过滤对象数组？

给定如下数组，其中部分对象的num和name字段组合存在重复，需要过滤掉一组num:"999"且name:"thing A"的重复项，最终返回4个对象：

{"array":[{"id":"1","num":"999","name":"thing A"},{"id":"2","num":"888","name":"thing A"},{"id":"3","num":"777","name":"thing B"},{"id":"4","num":"999","name":"thing A"},{"id":"5","num":"999","name":"thing B"}]}

实现思路 #

通过记录num与name的组合标识，遍历数组时只保留该组合第一次（或最后一次）出现的对象，即可完成双字段去重。

代码实现（JavaScript） #

1. 保留第一个出现的重复项（移除第4个对象）

const input = {"array":[{"id":"1","num":"999","name":"thing A"},{"id":"2","num":"888","name":"thing A"},{"id":"3","num":"777","name":"thing B"},{"id":"4","num":"999","name":"thing A"},{"id":"5","num":"999","name":"thing B"}]};

const seen = new Set();
const result = {
  array: input.array.filter(item => {
    const key = `${item.num}-${item.name}`;
    if (seen.has(key)) return false;
    seen.add(key);
    return true;
  })
};

console.log(JSON.stringify(result));

输出结果：

{"array":[{"id":"1","num":"999","name":"thing A"},{"id":"2","num":"888","name":"thing A"},{"id":"3","num":"777","name":"thing B"},{"id":"5","num":"999","name":"thing B"}]}

2. 保留最后一个出现的重复项（移除第1个对象）

const input = {"array":[{"id":"1","num":"999","name":"thing A"},{"id":"2","num":"888","name":"thing A"},{"id":"3","num":"777","name":"thing B"},{"id":"4","num":"999","name":"thing A"},{"id":"5","num":"999","name":"thing B"}]};

const seen = new Map();
// 遍历数组，记录每个组合最后出现的对象
input.array.forEach(item => {
  const key = `${item.num}-${item.name}`;
  seen.set(key, item);
});
// 将Map中的值转为数组
const result = { array: Array.from(seen.values()) };

console.log(JSON.stringify(result));

输出结果：

{"array":[{"id":"4","num":"999","name":"thing A"},{"id":"2","num":"888","name":"thing A"},{"id":"3","num":"777","name":"thing B"},{"id":"5","num":"999","name":"thing B"}]}

内容的提问来源于stack exchange，提问作者HobieKatz