el-table前两列内容一致时进行表格合并vue3+ts的写法
```
tableData: TableData[] = reactive([
{
actual: 'string',
assessmentMetric: 'string',
dateId: null,
description: null,
detailsId: null,
dotColor: 'string',
gaps: 1,
indicatorsId: 'string',
maxClass: '11111',
minClass: '22222',
objectives: 'string',
reached: 1,
total: 1,
type: 1
},
{
actual: 'string',
assessmentMetric: 'string',
dateId: null,
description: null,
detailsId: null,
dotColor: 'string',
gaps: 1,
indicatorsId: 'string',
maxClass: '11111',
minClass: '22222',
objectives: 'string',
reached: 1,
total: 1,
type: 1}])
```怎么样实现表格合并写法
