keep the last observation(s) in each year

[River Huang]

Dear All, Suppose that the data set is

* Example generated by -dataex-. To install: ssc install dataex
clear
input str6 Stkcd str10 riqi byte(Position Changtyp Edca Dimreas Dimage) double Years byte Entele
"000001" "2002-04-30" 1 1 4  . 56  3.17 .
"000001" "2003-09-04" 1 2 4  .  .     . 1
"000001" "2003-10-16" 2 1 4  3 52     6 .
"000001" "2003-10-16" 2 2 4  .  .     . 1
"000001" "2004-12-14" 1 1 4  3 53     1 .
"000001" "2004-12-14" 1 2 5  .  .     . 2
"000001" "2004-12-14" 2 1 4  3 42     1 .
"000001" "2004-12-14" 2 2 4  .  .     . 2
"000001" "2005-05-16" 1 1 5  5 62    .5 .
"000001" "2005-05-16" 1 2 3  .  .     . 1
"000001" "2005-06-17" 1 2 3  .  .     . 1
"000001" "2005-06-17" 1 1 3 12 62    .1 .
"000002" "2006-02-11" 2 1 4  5 53   1.1 .
"000002" "2007-02-07" 2 2 2  .  .     . 1
"000002" "2010-06-29" 1 1 3  5 68     5 .
"000002" "2010-06-29" 1 2 2  .  .     . 1
"000002" "2010-06-29" 2 1 2  1 62  3.33 .
"000002" "2010-06-29" 2 2 .  .  .     . 1
"000002" "2010-10-13" 2 1 . 12 54   .25 .
"000002" "2010-10-13" 2 2 .  .  .     . 1
"000002" "2012-11-21" 2 1 .  8 56  2.08 .
"000002" "2012-11-21" 2 2 5  .  .     . 2
"000002" "2012-11-21" 1 1 .  8 64  2.42 .
"000002" "2012-11-21" 1 2 2  .  .     . 2
"000003" "2016-10-20" 2 1 5  5 59  3.92 .
"000003" "2016-10-20" 2 2 4  .  .     . 1
"000003" "2016-11-06" 1 1 2  3 63  3.96 .
"000003" "2016-11-07" 1 2 4  .  .     . 1
"000003" "2016-12-10" 1 1 4 12 45   .09 .
"000003" "2016-12-10" 1 2 5  .  .     . 2
"000003" "2016-12-10" 2 1 4 12 54   .14 .
"000003" "2016-12-10" 2 2 4  .  .     . 1
"000003" "1999-02-08" 2 1 .  9 48     8 .
"000003" "1999-02-08" 2 2 3  .  .     . 1
"000004" "2001-02-15" 2 1 3  7 49     2 .
"000004" "2001-02-15" 2 2 4  .  .     . 1
"000004" "2002-06-12" 1 2 3  .  .     . 1
"000004" "2017-06-29" 1 1 3  3 66 15.06 .
"000004" "2017-06-30" 1 2 4  .  .     . 1
end

For each Stkcd and each year, I'd like to keep the last observation(s) occurred in each year.

Note that, if there are more than one observation with the same last date, keep them all. Thanks.

[Øyvind Snilsberg]

you could do,

gen year = yofd(date(riqi,"YMD"))
egen group = group(Stkcd year riqi)
bys Stkcd year: egen last = max(group)
keep if group == last

[Fei Wang]

Another solution as below.

gen date = date(riqi, "YMD")
gen year = yofd(date)
bys Stkcd year (date): keep if date == date[_N]

[River Huang]

Dear Øyvind, Thanks for this helpful suggestion.

[River Huang]

Dear Professor Wang, Thanks for this helpful suggestion.