使用Element的table合并单元格的问题（合并列）

官网案例：

<template>
  <div>
    <el-table
      :data="tableData"
      :span-method="objectSpanMethod"
      border
      style=" 100%; margin-top: 20px">
      <el-table-column
        prop="id"
        label="ID"
        width="180">
      </el-table-column>
      <el-table-column
        prop="name"
        label="姓名">
      </el-table-column>
      <el-table-column
        prop="amount1"
        label="数值 1（元）">
      </el-table-column>
      <el-table-column
        prop="amount2"
        label="数值 2（元）">
      </el-table-column>
      <el-table-column
        prop="amount3"
        label="数值 3（元）">
      </el-table-column>
    </el-table>
  </div>
</template>

<script>
  export default {
    data() {
      return {
        tableData: [{
          id: '12987122',
          name: '王小虎',
          amount1: '234',
          amount2: '3.2',
          amount3: 10
        }, {
          id: '12987123',
          name: '王小虎',
          amount1: '165',
          amount2: '4.43',
          amount3: 12
        }, {
          id: '12987124',
          name: '王小虎',
          amount1: '324',
          amount2: '1.9',
          amount3: 9
        }, {
          id: '12987125',
          name: '王小虎',
          amount1: '621',
          amount2: '2.2',
          amount3: 17
        }, {
          id: '12987126',
          name: '王小虎',
          amount1: '539',
          amount2: '4.1',
          amount3: 15
        }]
      };
    },
    methods: {     

      objectSpanMethod({ row, column, rowIndex, columnIndex }) {
        if (columnIndex === 0) {
          if (rowIndex % 2 === 0) {
            return {
              rowspan: 2,
              colspan: 1
            };
          } else {
            return {
              rowspan: 0,
              colspan: 0
            };
          }
        }
      }
    }
  };
</script>

我的代码：

objectSpanMethod({ row, column, rowIndex, columnIndex }) {
        if (column.property === "positionItemName" || column.property === "saName") { // 这部分是因为我需要切换合并的列
          if (rowIndex  === 0 ) {
            this.$nextTick(() => {
              this.$refs['table_2'].doLayout();
            })
            return {
              rowspan: this.keySATestAndDealData.length, // 根据数据长度合并
              colspan: 1
            };
          }else {
            return [0, 0]
          }
        }
      },