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st: Invalid syntax


From   "Clive Nicholas" <Clive.Nicholas@newcastle.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: Invalid syntax
Date   Fri, 21 Nov 2003 20:01:06 -0000 (GMT)

Just for your info, I get an 'invalid syntax' error message after
-egen max=rmax(conpc, labpc, ldmpc, natpc, othpc)-. Not sure why: that
ought to work. :-(

C.

> I'm going to ignore the possibilities of ties for first
> place.
>
> Suppose, contrary to fact, that there were just two
> parties. Then -conwin- would be 1 if the
> Conservatives won and  if Labour won, i.e.
>
> gen conwin = conpc > labpc
>
> or, more long-windedly,
>
> gen conwin = 1 if conpc > labpc
> replace conwin =  if conpc < labpc
>
> which has  and 1 reversed from what you have.
>
> When you bring in other parties, note that your extra
> conditions
>
> & ldmpc & natpc & othpc
>
> are read by Stata as
>
> & (ldmpc != 0) & (natpc != 0) & (othpc != 0)
>
> which is not what you want. Perhaps you are
> guessing that Stata will interpret
>
> & ldmpc & natpc & othpc
>
> as if it meant
>
> & (conpc > ldmpc) & (conpc > natpc) & (conpc > othpc)
>
> but that's not the way Stata works.
>
> So, in short, you went wrong (1) because  and 1 are the wrong
> way round and (2) you're misinterpreting how
> compound conditions are handled.
>
> There's some context at
> http://www.stata.com/support/faqs/data/trueorfalse.html
>
> Now Matt Dobra has already given another solution.
> Here's another, which is not better, but nevertheless
> shows a Stataish approach useful in many other problems.
>
> First, map from your names to others
>
> foreach p in con lab ldm nat oth {
> 	rename `p'pc pc`p'
> }
>
> Second, -reshape- to long
>
> reshape long pc, i(district) j(party) string
>
> Third,
>
> bysort district (pc) : gen win = _n == _N
>
> generates your -win- variable collectively.
>
> This works as follows:
>
> bysort district (pc) :
>
> sorts the winning party to the end
> of each block of observations,
> and in that context
>
> 	gen win = _n == _N
>
> puts win = 1 in the last observation and win =  in
> the others in each block.
>
> Fourth, -reshape- back:
>
> reshape wide pc win, i(district) j(party) string
>
> Fifth, if you prefer your names, map backwards:
>
> foreach p in con lab ldm nat oth {
> 	rename pc`p' `p'pc
> 	rename win`p' `p'win
> }
>
> So, given appropriate variable names, the code
> boils down to
>
> reshape long pc , i(district) j(party) string
> bysort district (pc) : gen win = _n == _N
> reshape wide pc win, i(district) j(party) string
>
> If you had a copy, [R] reshape would be
> a place to look. As it is, there are still
> examples you can look at in the on-line help
> and at
> http://www.stata.com/support/faqs/data/reshape3.html
> Some examples are very close to this problem.
>
> There was a tutorial on -by:- in Stata Journal 2(1)
> 86-102 (2002).
>
> Nick
> n.j.cox@durham.ac.uk
>
> P.S. I've supposed in all this that the data
> concern a single election. If there were
> several, then I think something like this would
> work (assuming an extra variable -year-):
>
> reshape long pc , i(district year) j(party) string
> bysort district year (pc) : gen win = _n == _N
> reshape wide pc win, i(district year) j(party) string
>
> The -reshape- brings real bonus whenever the "obvious"
> wide data structure turns out to be awkward for some
> manipulation (althugh it can be avoided, as in Matt
> Dobra's solution, in some cases by using -egen-
> functions).
>
> *
> *   For searches and help try:
> *   http://www.stata.com/support/faqs/res/findit.html
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>


Yours,
CLIVE NICHOLAS,
Politics Building,
School of Geography, Politics and Sociology,
University of Newcastle-upon-Tyne,
Newcastle-upon-Tyne,
NE1 7RU,
United Kingdom.
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



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