inlist2命令为什么做不了面板数据
. xtset id year
       panel variable:  id (strongly balanced)
        time variable:  year, 2011 to 2020
                delta:  1 unit

. inlist2 city, values(四川,贵州,云南,西藏,陕西,甘肃,青海,宁夏,重庆,新疆)


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