将平级数据变为树结构

Unflatten

// 将平级数据变为树结构
const arr = [{
	id:1,
  parent: null,
},{
	id:2,
  parent: null,
},{
	id: 3,
  parent: {id:1}
},{
	id: 4,
  parent: {id:1}
},{
	id:5,
  parent: null
}]

const Unflatten = arr => {
  if (arr.length === 0) {
    return [];
  }
  const tree = [];
  const mappedArr = {};
  let arrElem;
  let mappedElem;

  for (let i = 0, len = arr.length; i < len; i += 1) {
    arrElem = arr[i];
    mappedArr[arrElem.id] = arrElem;
    mappedArr[arrElem.id].children = [];
  }

  Object.keys(mappedArr).forEach(id => {
    mappedElem = mappedArr[id];
    if (mappedElem.parent && mappedElem.parent.id) {
      if (mappedArr[mappedElem.parent.id]) {
        mappedArr[mappedElem.parent.id].children.push(mappedElem);
      }
    } else {
      tree.push(mappedElem);
    }
  });

  return tree;
};
console.log(Unflatten(arr));