Node.js，通过对象数组进行映射，并将特定值放入新数组答案

【问题标题】：Node.js, map through array of objects, and put specific values into a new arrayNode.js，通过对象数组进行映射，并将特定值放入新数组
【发布时间】：2020-04-25 01:54:32
【问题描述】：

我正在尝试遍历每个对象的评级数组，提取每个内部对象的分数并将它们添加到一个新数组中。

例如，post_id 为“5e1223c2383ce049d8b32eb5”的帖子，我需要一个包含 [1, 4] 的关联数组。和带有 post_id" "5e146b993dde720850c11c0e" 的帖子将包含 [5] 等。

我们将不胜感激！

[
    {
        "post_id": "5e1223c2383ce049d8b32eb5",
        "ratings": [
            {
                "_id": "5e134aa9d6c3a51930452d49",
                "user": "5e0f76c96a55d6352879daab",
                "score": 1
            },
            {
                "_id": "5e134c00cab61f408c75d2f2",
                "user": "5e0f34adab4d4b369c57fbd4",
                "score": 4
            }
        ]
    },
    {
        "post_id": "5e13592c62008b4e3435472f",
        "ratings": []
    },
    {
        "post_id": "5e146b993dde720850c11c0e",
        "ratings": [
            {
                "_id": "5e1473583dde720850c11c13",
                "user": "5e0f34adab4d4b369c57fbd4",
                "score": 5
            }
        ]
    }
]

【问题讨论】：

您的预期输出是什么？ {"5e1223c2383ce049d8b32eb5" : [1, 4]}?

标签： javascript arrays node.js sorting

【解决方案1】：

    const original_array = [
        {
            "post_id": "5e1223c2383ce049d8b32eb5",
            "ratings": [
                {
                    "_id": "5e134aa9d6c3a51930452d49",
                    "user": "5e0f76c96a55d6352879daab",
                    "score": 1
                },
                {
                    "_id": "5e134c00cab61f408c75d2f2",
                    "user": "5e0f34adab4d4b369c57fbd4",
                    "score": 4
                }
            ]
        },
        {
            "post_id": "5e13592c62008b4e3435472f",
            "ratings": []
        },
        {
            "post_id": "5e146b993dde720850c11c0e",
            "ratings": [
                {
                    "_id": "5e1473583dde720850c11c13",
                    "user": "5e0f34adab4d4b369c57fbd4",
                    "score": 5
                }
            ]
        }
    ];
    
    const new_array = original_array.map(item => ({
        post_id: item.post_id,
        ratings: item.ratings.map(item => item.score)
    }));
    
    console.log(new_array);

输出：

[
    {
        post_id: '5e1223c2383ce049d8b32eb5',
        ratings: [1, 4]
    },
    {
        post_id: '5e13592c62008b4e3435472f',
        ratings: []
    },
    {
        post_id: '5e146b993dde720850c11c0e',
        ratings: [5]
    }
]

【讨论】：

最后一行的“=>”有什么作用？这是什么意思？
@MoltasDev，这是一个arrow function
@MoltasDev 它基本上是function(item) { return item.score; } 的简写方式。 ES6 语法。或者也可以写成item => { return item.score; }等等。
@decho ...但不完全相同
@Ivan 和 VLAZ 我知道这一点，但您不可能以简短答案的形式涵盖所有可能的细节。所以是的，箭头函数不是常规函数的复本，但在问题的上下文中，它们具有相同的目的。

【解决方案2】：

您可以遍历帖子数组并将每个用户数组映射到分数数组：

data.forEach(post => {
  post.ratings = post.ratings.map(({score}) => score)
});

console.log(data)

&lt;script&gt;const data=[{post_id:"5e1223c2383ce049d8b32eb5",ratings:[{_id:"5e134aa9d6c3a51930452d49",user:"5e0f76c96a55d6352879daab",score:1},{_id:"5e134c00cab61f408c75d2f2",user:"5e0f34adab4d4b369c57fbd4",score:4}]},{post_id:"5e13592c62008b4e3435472f",ratings:[]},{post_id:"5e146b993dde720850c11c0e",ratings:[{_id:"5e1473583dde720850c11c13",user:"5e0f34adab4d4b369c57fbd4",score:5}]}];&lt;/script&gt;

您还可以映射整个数组以创建一个单独的对象：

const result = data.map(({ post_id, ratings }) => {
  return { post_id, ratings: ratings.map(({ score }) => score) }
});

console.log(result)

&lt;script&gt;const data=[{post_id:"5e1223c2383ce049d8b32eb5",ratings:[{_id:"5e134aa9d6c3a51930452d49",user:"5e0f76c96a55d6352879daab",score:1},{_id:"5e134c00cab61f408c75d2f2",user:"5e0f34adab4d4b369c57fbd4",score:4}]},{post_id:"5e13592c62008b4e3435472f",ratings:[]},{post_id:"5e146b993dde720850c11c0e",ratings:[{_id:"5e1473583dde720850c11c13",user:"5e0f34adab4d4b369c57fbd4",score:5}]}];&lt;/script&gt;

【讨论】：