st: Use egen command with time series operator

["Klepsch, Catharina" <klepsch@bwl.lmu.de>]

Dear Stata Users,

I was wondering whether it is possible to use the egen command with time series operators. 
For example, I tried to generate the mean value for a lagged variable and used:

sort ID YEAR
egen mean_x1 = mean(l.x1)

Unfortunately, there occurs an error message which states: 
not sorted r(5)

I'm not quite sure why this happens, because I sorted the data before. Even if I type:
bys ID YEAR: egen mean_x1 = mean(l.x1)

the same error message occurs.

Any ideas how I can fix that? Please consider that it is not reasonable for my programming to first generate the lag/lead and then generate the mean.

Thank's for any help.
Catharina





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