各位大神好，我有一个问题就是我使用reshape 命令将横着的数据变成竖着的时候 出错了 请问有大神帮忙看看怎么办吗？
reshape long inv , i(city) j(year)  inv是专利授权量 这个表格里的数据就是各个年份各个城市的专利授权量
no xij variables found
    You typed something like reshape wide a b, i(i) j(j).
    reshape looked for existing variables named a# and b# but could not find any. Remember this picture:
long to wide: reshape wide a b, i(i) j(j)    (j existing variable)
        wide to long: reshape long a b, i(i) j(j)    (j new variable)