Listing unique observations with a rolling window

Dear all,

Suppose I have the following dataset:

Code:

clear
input  str8 memberid year
"B000" 1980
"B001" 1980
"B002" 1980
"B001" 1981
"B002" 1981
"B003" 1981
"B004" 1981
"B000" 1982
"B003" 1982
"B005" 1982
"B004" 1983
"B005" 1983
"B002" 1984
"B005" 1985
"B006" 1985
"B015" 1984
"B018" 1985
"B019" 1985
"B017" 1986
"B019" 1986
"B000" 1987
"B000" 1988
"B005" 1989
end

I'd would like to create a variable to store unique values for memeberid over the past three years. I have tried the following set of code but it fails to work.

Code:

encode memberid, gen(nmemberid) label(lmemberid)
program lunique
 quietly levelsof nmemberid
 gen  luniqueid="`r(levels)'"
end

rangerun lunique, use(nmemberid) interval(year -2 0)

Could anyone please help me with this ?

Thank you very much for your help,

Vinh