通过包含在数组中的对象的属性将对象数组分组为二维数组答案

【问题标题】：Group Array of objects into 2D Array by the property of an object contained into an array通过包含在数组中的对象的属性将对象数组分组为二维数组
【发布时间】：2022-12-18 17:18:43
【问题描述】：

我有一组这样的对象：

[
  {
    "id": 1,
    "name": "Question1",
    "categories": [
      {
        "id": 20,
        "name": "Science"
      },
      {
        "id": 21,
        "name": "General Knowledge"
      },
      {
        "id": 20,
        "name": "Mathematic"
      }
    ]
  },
  {
    "id": 2,
    "name": "Question2",
    "categories": [
      {
        "id": 20,
        "name": "Science"
      }
    ]
  },
  {
    "id": 3,
    "name": "Question3",
    "categories": [
      {
        "id": 20,
        "name": "Science"
      }
    ]
  }
]

我想按对象属性将对象分组为子数组（按字母顺序排序）姓名数组的类别.

预期的输出将是：

[
  //General Knowledge
  [
    {
      "id": 1,
      "name": "Question1",
      "categories": [
        {
          "id": 20,
          "name": "Science"
        },
        {
          "id": 21,
          "name": "General Knowledge"
        },
        {
          "id": 20,
          "name": "Mathematic"
        }
      ]
    }
  ],
  //Mathematic
  [
    {
      "id": 1,
      "name": "Question1",
      "categories": [
        {
          "id": 20,
          "name": "Science"
        },
        {
          "id": 21,
          "name": "General Knowledge"
        },
        {
          "id": 20,
          "name": "Mathematic"
        }
      ]
    }
  ],
  //Science
  [
    {
      "id": 1,
      "name": "Question1",
      "categories": [
        {
          "id": 20,
          "name": "Science"
        },
        {
          "id": 21,
          "name": "General Knowledge"
        },
        {
          "id": 20,
          "name": "Mathematic"
        }
      ]
    },
    {
      "id": 2,
      "name": "Question2",
      "categories": [
        {
          "id": 20,
          "name": "Science"
        }
      ]
    },
    {
      "id": 3,
      "name": "Question3",
      "categories": [
        {
          "id": 20,
          "name": "Science"
        }
      ]
    }
  ]
]

我一直在尝试使用循环和Array.reduce()，但我没能成功。

哪一个是实现预期输出的最佳方式？非常感谢！

【问题讨论】：

你能确认你的预期输出是正确的吗？您不是说问题 1 每次只有常识，然后只有数学，然后只有科学，而不是这三个吗？
预期的输出是正确的，因为每个子数组都是一个组。问题 1 重复三次（每个数组重复一次）因为它有三个类别

标签： javascript arrays sorting grouping lodash

【解决方案1】：

遍历每个对象并在该循环中遍历 categories。在 group 对象中使用每个类别名称作为键，并使用一组问题作为值

const group = {}

for (const q of questions) {
  for(const c of q.categories) {
    group[c.name] ??= []
    group[c.name].push(q)
  }
}

const output = Object.values(group)

这是一个 sn-p：

const questions =[{id:1,name:"Question1",categories:[{id:20,name:"Science"},{id:21,name:"General Knowledge"},{id:20,name:"Mathematic"}]},{id:2,name:"Question2",categories:[{id:20,name:"Science"}]},{id:3,name:"Question3",categories:[{id:20,name:"Science"}]}];

const group = {}

for (const q of questions) {
  for(const c of q.categories) {
    group[c.name] ??= []
    group[c.name].push(q)
  }
}

const output = Object.values(group)

document.querySelector("pre").innerText = JSON.stringify(output, null, 4)

&lt;pre /&gt;

【讨论】：

【解决方案2】：

假设您的预期输出是正确的，这就是我所做的。我不知道这是最有效的方法，但它有效：

const input = [
  {
    id: 1,
    name: "Question1",
    categories: [
      {
        id: 20,
        name: "Science",
      },
      {
        id: 21,
        name: "General Knowledge",
      },
      {
        id: 20,
        name: "Mathematic",
      },
    ],
  },
  {
    id: 2,
    name: "Question2",
    categories: [
      {
        id: 20,
        name: "Science",
      },
    ],
  },
  {
    id: 3,
    name: "Question3",
    categories: [
      {
        id: 20,
        name: "Science",
      },
    ],
  },
];

// First we put all subjects into an array.
const subjects = [];
for (const element of input) {
  for (const categories of element.categories) {
    if (!subjects.find((e) => e === categories.name)) {
      subjects.push(categories.name);
    }
  }
}

// then we add the element to our output ordered by subjet
const output = [];
for (const subject of subjects) {
  const tempOutput = [];
  for (const element of input) {
    if (element.categories?.find((e) => e.name === subject)) {
      tempOutput.push(element);
    }
  }
  output.push(tempOutput);
}

console.log(output);

【讨论】：

【解决方案3】：

const convert = (input) => {
        return input.reduce((acc, question) => {
            question.categories.forEach((category) => {
            if (!acc[category.id]) {
                acc[category.id] = [];
            }
            acc[category.id].push(question);
            });
            return acc;
        }, []);
        };

使用此功能

【讨论】：