想做一个panel data的analysis，原始数据有number of household, index of family member，于是我想用这2个变量成为一个新的确定个人的variable: nohholdnomem

原始的这两个数据都是数据型的，无法gen a new variable ,于是我先将number of household, index of family member 2个变量变成了string type
而后
gen gen nohholdnomem =  nohhold + " " +  nomem

之后xtset 的时候有问题了
xtset nohholdnomem year
varlist:  nohholdnomem:  string variable not allowed
r(109);

于是
. destring  nohholdnomem, replace
nohholdnomem contains nonnumeric characters; no replace

再次xtset依旧失败、

请大虾指教该如何修改。。。谢谢！