'not sorted': Generate variable by group

[Feuer Salamander]

Hello,

I have a dataset such that my panel consists of country i industry j and year t. My main explanatory variable is x. I would like to generate a variable x_mean that is defined as the meanover the previous periods by country.

I tried to do the following:

xtset panelid year (where panelid has dimension ij)
gen x_mean =.
bysort country: replace x_mean = L1.x if year == 1962
bysort country: replace x_mean = (L1.x + L2.x)/2 if year == 1963
etc.

However, I get the error message "not sorted r(5);"

I already tried to first write "sort country" or "sort country year" or "sort country industry year". But I still get the same error message.

Could anyone please help me with coding the mean over previous previous by country?

Thank you!

[Nick Cox]

Once you have xtset using by: as well is unnecessary and can even conflict with using time series operators.

replace x_mean = L1.x if year == 1962

replace x_mean = (L1.x + L2.x)/2 if year == 1963