st: re: keep longest consecutive streak (recently broken by Red Sox)

[Kit Baum <baum@bc.edu>]

Nick said

More instructive in some ways is to
do it from scratch, with no use of user
add-ons. Something like

gen spell = sum(L.time == .)
bysort firm spell : gen length = _N
bysort firm length (time) : keep if spell == spell[_N]

Nice, except that it does not work:

       |---------------------------|
  358. |   10404   1987   .0511182 |
  359. |   10404   2002   .0337511 |
  360. |   10404   2003   .0296446 |
       |---------------------------|

This firm has the original observations

       +---------------------------+
       | npermno   year        ita |
       |---------------------------|
  358. |   10404   1987   .0511182 |
  359. |   10404   1989   .0159272 |
  360. |   10404   1990   .0455364 |
  361. |   10404   1992   .0097333 |
  362. |   10404   1993   .0231792 |
  363. |   10404   1995   .0534575 |
  364. |   10404   1996   .0622322 |
  365. |   10404   2002   .0337511 |
  366. |   10404   2003   .0296446 |
       +---------------------------+

By coincidence, I have been working during the last 24 hours on an 
ado-file that does this "keep longest streak", but does it listwise for 
an entire variable list, as is required by some matrix software (that 
is, we need to generate the longest streak for which NONE of these 
variables are missing). It also deals with the case, as above, where 
the longest streak is tied; as an earlier posting suggests, the latest 
streak should be retained (which is what my code does). I'm pretty sure 
that it works, but I have given it to Nick to see if he can break it.

Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html

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