element-ui操作表格行内容如何获取当前行索引？

需求：

根据每个用户的提交次数、撤回次数，动态计算出实际次数，并且提交次数不能小于撤回次数

<template><div><el-table:data="tableData"style="width: 80%"border><el-table-columnprop="date"label="日期"width="120"></el-table-column><el-table-columnprop="name"label="姓名"width="120"></el-table-column><el-table-columnprop="address"label="地址"width="250"></el-table-column><el-table-columnprop="submitNumber"label="提交次数"width="180"><template slot-scope="scope"><el-input-number v-model="scope.row.submitNumber" size="small" :min="scope.row.withdrawNumber" label="描述文字" @change="(currentValue)=>setProNum(currentValue,scope.$index)"></el-input-number></template></el-table-column><el-table-columnprop="withdrawNumber"label="撤回次数"></el-table-column><el-table-columnprop="actualNumber"label="实际次数"></el-table-column></el-table></div>
</template><script>
export default {name: 'TableRowIndex',data() {return {tableData: [{date: '2016-05-02',name: '王小虎',address: '上海市普陀区金沙江路 1518 弄',submitNumber:34,withdrawNumber:2,actualNumber:32,}, {date: '2016-05-04',name: '王小虎',address: '上海市普陀区金沙江路 1517 弄',submitNumber:6,withdrawNumber:3,actualNumber:3,}, {date: '2016-05-01',name: '王小虎',address: '上海市普陀区金沙江路 1519 弄',submitNumber:13,withdrawNumber:7,actualNumber:6,}, {date: '2016-05-03',name: '王小虎',address: '上海市普陀区金沙江路 1516 弄',submitNumber:34,withdrawNumber:12,actualNumber:22,}]};},methods: {setProNum(currentValue, index){this.tableData[index].actualNumber = currentValue - this.tableData[index].withdrawNumber},},
};
</script>