vue 数组对象分组

 this.ProjectGroupList = this.groupBy(this.ProjectList, function(item) {
          return [item.ParentID];
        });

 groupBy: function(array, f) {
      let groups = {};
      array.forEach(function(o) {
        let group = JSON.stringify(f(o));
        groups[group] = groups[group] || [];
        groups[group].push(o);
      });
      return Object.keys(groups).map(function(group) {
        return groups[group];
      });
    },