elementui el-table某列合并

<el-table  size='medium' border :data="tableData" :span-method="objectSpanMethod">
setFirstName(arr) {
      this.arr1 = []
      var obj = {},
        k
      for (var i = 0, len = arr.length; i < len; i++) {
        k = arr[i].firstName
        if (obj[k]) {
          obj[k]++
        } else {
          obj[k] = 1
        }
      }
      console.log(obj)   // {福建省人民医院: 10}
      //保存结果{el-'元素'，count-出现次数}
      for (var o in obj) {
        for (let i = 0; i < obj[o]; i++) {
          if (i === 0) {
            this.arr1.push(obj[o])
          } else {
            this.arr1.push(0)
          }
        }
      }
},
objectSpanMethod({ row, column, rowIndex, columnIndex }) {
        if (columnIndex === 0) {
          return {
            rowspan: this.arr1[rowIndex],
            colspan: 1
          };
        } 
}