求教下面的那个变量如何在stata中实现：
|iki,t-ik-i,t-1| is the absolute value of the difference between ik (the investment ratio) of firm i in year t and the average (第二个ik 上面应该有个横杠，不知道怎么弄出来) investment ratio of other firms in the same industry excluding firm i in year (t-1)
PS：数据为panel data，包括firmid，year，ik等数据
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