Replace value

[Daniel Gomez]

Hi!

How can I replace the value of one variable X in period T for the value of the variable X in the previous period T-1?

replace X = ??? if year ???

Thanks!

[Joseph Coveney]

Why not just add 1 to the year?

replace year = year + 1

[Jorrit Gosens]

What Joseph suggests would do the same operation for all variables, not just a single one.
You can do, assuming it is panel data:

bysort id year: replace x = x[_n-1]

And note also that Stata allows time operators in regressions, which means ha in most cases you do not have to manually create lagged variables.
Example:

xtreg outcome varY varZ L1.varX

[Nick Cox]

Jorrit Gosens is pointing in a good direction but the code would be better as

bysort id (year) :

and the replacement should be conditional if missing(x). it needs to be more complicated still if there are gaps in the data.

[Nick Cox]

The best approach is probably

tsset id year 
replace x = L.x if missing(x)

There is a wider discussion at https://www.stata.com/support/faqs/d...issing-values/ . But even if interpolation is a good idea, there may well be better ways to do it.