Example of converting JS one-dimensional array into three-dimensional array

 let arr = [{
      'peovince': 'a', 'city': 'b', 'area': 'c'
    },
    {
      'peovince': 'a', 'city': 'b', 'area': 'd'
    },
    {
      'peovince': 'a', 'city': 'e', ​​'area': 'f'
    },
    {
      'peovince': 'a', 'city': 'e', ​​'area': 'g'
    },
    {
      'peovince': 'o', 'city': 'p', 'area': 'q'
    },
    {
      'peovince': 'o', 'city': 'p', 'area': 'r'
    },
    {
      'peovince': 'o', 'city': 's', 'area': 't'
    },
    {
      'peovince': 'o', 'city': 's', 'area': 'v'
    }];

let list = Array.from(new Set(
      arr.map(item => {
        return item['peovince']
      })))
    let subList = []
    list.forEach(res => {
      arr.forEach(ele => {
        if (ele['peovince'] === res) {
          let nameArr = subList.map(item => item.value)
          if (nameArr.indexOf(res) !== -1) {
            let nameArr2 = subList[nameArr.indexOf(res)].children.map(item => item.value)
            if (nameArr2.indexOf(ele['city']) !== -1) {
              subList[nameArr.indexOf(res)].children[nameArr2.indexOf(ele['city'])].children.push({
                value: ele['area'],
                label:ele['area'],
              })
            } else {
              subList[nameArr.indexOf(res)].children.push({
                value: ele['city'],
                label:ele['city'],
                children: [{
                  value: ele['area'],
                  label:ele['area'],
                }]
              })
            }
          } else {
            subList.push({
              value: res,
              label: res,
              children: [{
                value: ele['city'],
                label:ele['city'],
                children: [{
                  value: ele['area'],
                  label:ele['area'],
                }]
              }]
            })
          }
        }
      })

    })
    console.log(subList)

  let array = [1, 2, 3, 4, 5, 6, 7, 8];
  len len = array.length;
  let n = 4; //Assume that 4 items are displayed per line let lineNum = len % n === 0 ? len / n : Math.floor( (len / n) + 1 );
  let res = [];
  for (let i = 0; i < lineNum; i++) {
    // The slice() method returns a shallow copy of a portion of an array selected from the beginning to the end (excluding the end) into a new array object. The original array will not be modified.
    let temp = array.slice(i*n, i*n+n);
    res.push(temp);
  }
  console.log(res);

  let objArray = [{a: 1}, {b: 2}, {c: 3}, {d: 4}, {e: 5}, {f: 6}, {g: 7}];
  let len ​​= objArray.length;
  let n = 4; //Assume that 4 items are displayed per line let lineNum = len % 4 === 0 ? len / 4 : Math.floor( (len / 4) + 1 );
  let res = [];
  for (let i = 0; i < lineNum; i++) {
    let temp = objArray.slice(i*n, i*n+n);
    res.push(JSON.parse(JSON.stringify(temp)));
  }
  console.log(res);