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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Winning and losing |

Date |
Fri, 21 Nov 2003 11:56:53 -0000 |

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 0 if Labour won, i.e. gen conwin = conpc > labpc or, more long-windedly, gen conwin = 1 if conpc > labpc replace conwin = 0 if conpc < labpc which has 0 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 0 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 = 0 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/

**Follow-Ups**:**st: Invalid syntax***From:*"Clive Nicholas" <Clive.Nicholas@newcastle.ac.uk>

**Re: st: RE: Winning and losing***From:*"Clive Nicholas" <Clive.Nicholas@newcastle.ac.uk>

**Re: st: RE: Winning and losing***From:*"Clive Nicholas" <Clive.Nicholas@newcastle.ac.uk>

**References**:**st: Winning and losing***From:*"Clive Nicholas" <Clive.Nicholas@newcastle.ac.uk>

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