As Henry Kelly might have asked on "Going For Gold", what 'T' am I?!
(DON'T answer that one!! *lol*)
Apologies, folks: I did indeed get my codes wrong; and that might well be
where I've gone wrong. Apologies for any confusion caused. Amazing how
many things you can get wrong when you do execute tasks at high speed!
Thanks to all of you for your solutions: I'll have fun trying them out! :-)
C.
> Clive Nicholas
>
>> I'm looking to dummy-code (0/1) which party won
>> the ith seat in the jth election. Since this is Blighty,
>> there can only be
>> one winner per district, but since that n=3452, that's an
>> awful lot of
>> outcomes to code manually! There are five outcome
>> categories: conwin;
>> labwin; ldmwin; natwin; and othwin.
>>
>> Now here's the rub: since it's plurality-rule, I need to
>> tell Stata to
>> code, say, conwin=1 and labwin-othwin=0 if, say, for
>> district X: conpc=35;
>> labpc=31; ldmpc=16; natpc=17; othpc=1. I've tried several
>> generates, such
>> as:
>>
>> -g conwin=0 if conpc > labpc & ldmpc & natpc & othpc-
>> -replace conwin=1 if conpc < labpc & ldmpc & natpc & othpc-,
>>
>> but, although Stata did not return errors at *any* of my
>> 'solutions', each
>> kept producing multiple, rather than unique, 1's for each
>> case (or n).
>>
>> Any ideas as to where I'm going wrong?
>
> 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
> [email protected]
>
> 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/
