Find first non-missing str value in panel & use value to forward and back fill by group (SAS or PROC SQL)

Question

I have a data set containing an unbalanced panel of observations, where I want to forward and backward fill missing and/or \"wrong\" observations of ticker with the latest non-m

Answer 1

You can do this several ways, but proc sql with some nested sub-queries is one solution.

(Read it from inside out, #1 then 2 then 3. You could build each subquery into a dataset first if it helps)

proc sql ;
  create table want as 
  /* #3 - match last ticker on id */
  select a.id, a.time, a.ticker_have, b.ticker_want
  from have a
       left join
        /* #2 - id and last ticker */
       (select x.id, x.ticker_have as ticker_want
        from have x
             inner join
              /* #1 - max time with a ticker per id */
             (select id, max(time) as mt
              from have
              where not missing(ticker_have)
              group by id) as y on x.id = y.id and x.time = y.mt) as b on a.id = b.id
  ;
quit ;