如何对嵌套数组中的每个项进行分组

Question

我有一个json数组的表单：

    [{
        "published": true,
        "tags": ["tag1", "tag2"],
        "categories": ["cat1"],
        "author": "some name",
        "post-format": "standard",
        "title": "Second Post,",
        "url-slug": "second-post",
        "first-published-on": "2019-03-28",
        "last-updated-on": "2019-03-28",
        "meta": {
            "title": "Second Post",
            "description": "Second post."
        },
        "excerpt": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt",
        "path": "2019/03/28/SecondPost.md"
    }, {
        "published": true,
        "tags": ["tag1", "tag2", "tag3"],
        "categories": ["cat1", "cat2"],
        "author": "some name",
        "post-format": "standard",
        "title": "Getting Started",
        "url-slug": "getting-started",
        "first-published-on": "2019-03-20",
        "last-updated-on": "2019-03-20",
        "meta": {
            "title": "Getting Started",
            "description": "Getting started post."
        },
        "excerpt": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt",
        "path": "2019/03/20/GettingStarted.md"
    }]

我想将它们按标签分组，形式如下：

[{
   "tag1": [{...}, {...}], 
   "tag2": [{...}, {...}], 
   "tag3": [{...}]
}]

我曾尝试这样做：

const groupedByTag = _.groupBy(blogMetadata, function(postmetadata) {
        postmetadata.tags.map(tag => {
          return tag
        })
      })

显然，上面的代码是不正确的，不起作用。我看过一个相关的post，但没有取得多大进展。任何帮助都是非常感谢的。

Answer 1

您可以使用reduce和forEach

这里的想法是

• 首先，我们循环遍历obj变量的每个元素。
• 对于每个元素，我们循环遍历tags属性。
• 我们检查op是否已经有那个标记，然后按下值，否则就会向op对象添加一个新的键，并相应地添加相应的值。

​

let obj = [{"published": true,"tags": ["tag1", "tag2"],"categories": ["cat1"],"author": "some name","post-format": "standard","title": "Second Post,","url-slug": "second-post","first-published-on": "2019-03-28","last-updated-on": "2019-03-28","meta": {"title": "Second Post","description": "Second post."},"excerpt": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt","path": "2019/03/28/SecondPost.md"}, {"published": true,"tags": ["tag1", "tag2", "tag3"],"categories": ["cat1", "cat2"],"author": "some name","post-format": "standard","title": "Getting Started","url-slug": "getting-started","first-published-on": "2019-03-20","last-updated-on": "2019-03-20","meta": {"title": "Getting Started","description": "Getting started post."},"excerpt": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt","path": "2019/03/20/GettingStarted.md"}]

let final = obj.reduce((op,inp) => {
  inp.tags.forEach(e => {
    op[e] = op[e] || []
    op[e].push(JSON.parse(JSON.stringify(inp)))
  }) 
  return op
},{})

console.log(final)

​