javascript - 如何在 JavaScript 中的对象数组中标记具有重复属性的第一个对象

Question

我有一个像这样的数组:

 var myArray = [
    {id: 1, entry_id: 1, name: 'test', email: 'foo@bar.com'},
    {id: 2, entry_id: 1, name: 'test', email: 'bar@foo.com'},
    {id: 3, entry_id: 2, name: 'test', email: 'foo@bar.com'},
    {id: 4, entry_id: 2, name: 'test', email: 'bar@foo.com'},
    {id: 5, entry_id: 3, name: 'test', email: 'joe@ocean.com'},
    {id: 6, entry_id: 3, name: 'test', email: 'foo@bar.com'},
    {id: 7, entry_id: 3, name: 'test', email: 'foo@bar.com'},
 ];

我需要用相同的“entry_id”和“name”来标记哪个元素是第一个，所以结果应该是这样的:

 [
    {id: 1, entry_id: 1, name: 'test', email: 'foo@bar.com', isFirst:true},
    {id: 2, entry_id: 1, name: 'test', email: 'bar@foo.com', isFirst:false},
    {id: 3, entry_id: 2, name: 'test', email: 'foo@bar.com', isFirst:true},
    {id: 4, entry_id: 2, name: 'test', email: 'bar@foo.com', isFirst:false},
    {id: 5, entry_id: 3, name: 'test', email: 'joe@ocean.com', isFirst:true},
    {id: 6, entry_id: 3, name: 'test', email: 'foo@bar.com', isFirst:false},
    {id: 7, entry_id: 3, name: 'test', email: 'foo@bar.com', isFirst:false},
 ];

我已经尝试过:

function updateArray() {
    myArray.forEach((item, i) => {
      item.isFirst = false;
      myArray.forEach((item2, j) =>{
        if (item.entry_id == item2.entry_id && item.name == item2.name && i < j ) {
          item.isFirst = true;
        } else if (!item.isFirst) {
          item.isFirst = false;
      }
   })
 })
 return myArray;
}

我得到的结果如下:

 [
    {id: 1, entry_id: 1, name: 'test', email: 'foo@bar.com', isFirst:true},
    {id: 2, entry_id: 1, name: 'test', email: 'bar@foo.com', isFirst:false},
    {id: 3, entry_id: 2, name: 'test', email: 'foo@bar.com', isFirst:true},
    {id: 4, entry_id: 2, name: 'test', email: 'bar@foo.com', isFirst:false},
    {id: 5, entry_id: 3, name: 'test', email: 'joe@ocean.com', isFirst:true},
    {id: 6, entry_id: 3, name: 'test', email: 'foo@bar.com', isFirst:true},
    {id: 7, entry_id: 3, name: 'test', email: 'foo@bar.com', isFirst:false},
 ];

有没有比使用 2 个循环更好的方法？

感谢您的帮助!

链接到jsfiddle: https://jsfiddle.net/88p5p5oj/30/

Answer 1

您可以使用哈希表在单个循环中收集所需组的第一个标志。

var array = [{ id: 1, entry_id: 1, name: 'test', email: 'foo@bar.com' }, { id: 2, entry_id: 1, name: 'test', email: 'bar@foo.com' }, { id: 3, entry_id: 2, name: 'test', email: 'foo@bar.com' }, { id: 4, entry_id: 2, name: 'test', email: 'bar@foo.com' }, { id: 5, entry_id: 3, name: 'test', email: 'joe@ocean.com' }, { id: 6, entry_id: 3, name: 'test', email: 'foo@bar.com' }, { id: 7, entry_id: 3, name: 'test', email: 'foo@bar.com' }],
    keys = ['entry_id', 'name'],
    hash = Object.create(null);

array.forEach(o => {
    var key = keys.map(k => o[k]).join('|');
    o.isFirst = !hash[key];
    hash[key] = true;
});

console.log(array);

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