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RE: st: question: how do i...


From   Keith Dear <keith.dear@anu.edu.au>
To   statalist@hsphsun2.harvard.edu
Subject   RE: st: question: how do i...
Date   Mon, 07 Mar 2005 16:45:09 +1100

This is a good game...

egen maxscore = rmax(votesA votesB votesC votesD)
gen second=.
foreach i of any A B C D {
  replace second=max(second,votes`i') if votes`i'<maxscore
}
gen margin=maxscore-second

Keith


At 03:40 PM 7/3/05, you wrote:
global lst "A B C D"
egen maxscore = rmax(votesA votesB votesC votesD)
foreach i of global lst {
gen diff`i'= maxscore - votes`i'
replace diff`i'=. if diff`i'==0
}
egen margin_of_victory = rmin(diffA diffB diffC diffD)

Anirban

-----Original Message-----
From: Phil Schumm
To: statalist@hsphsun2.harvard.edu
Sent: 3/6/2005 8:54 PM
Subject: Re: st: question: how do i...

At 1:53 AM +0000 3/7/05, israel solaresbravo wrote:
>i want to construct a variable called margin of victory:
>
>my data set looks something like this:
>
>
>margin_of_victory>
>
>my question is:
>
>how do i create a variable called margin_of_victory = votes for 1st
>place - votes for 2nd place?, i.e. 21-10 for state 1, 22 - 11 for
>state 2, 13 - 12 for state 3, 4 - 3 for state 4, etc.


If you reshape your data from wide to long form, then this is a snap.
Here are your data:

. li

      +-------------------------------------------+
      | state   votesa   votesb   votesc   votesd |
      |-------------------------------------------|
   1. |     1       10        1        6       21 |
   2. |     2       11        2        7       22 |
   3. |     3       12        3        8       13 |
   4. |     4        1        4        2        3 |
   5. |     5        2        5        3        7 |
      +-------------------------------------------+

Now, try the following (output omitted):

. reshape long votes, i(state) j(candidate) string
. bys state (votes): gen margin = votes[_N] - votes[_N-1]
. reshape wide

which produces exactly what you want:

. li

      +----------------------------------------------------+
      | state   votesa   votesb   votesc   votesd   margin |
      |----------------------------------------------------|
   1. |     1       10        1        6       21       11 |
   2. |     2       11        2        7       22       11 |
   3. |     3       12        3        8       13        1 |
   4. |     4        1        4        2        3        1 |
   5. |     5        2        5        3        7        2 |
      +----------------------------------------------------+

As you can see, the trick is in using -reshape-.  If you're not
familiar with what -reshape- does, use -list- after the first reshape
and take a look, then read [R] reshape.  Once the data are in long
form, we sort by state and number of votes, and then within each
state, compute the difference between the largest number of votes and
the next largest (hint: _N refers to the total number of observations
within the state, and votes[_N] is the last observation within the
state (which, since the observations are sorted by number of votes,
is the observation with the largest vote count)).


-- Phil
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==========================================================
Dr Keith B.G. Dear
Senior Fellow in Biostatistics
National Centre for Epidemiology and Population Health (NCEPH)
The Australian National University
Canberra, ACT 0200, Australia
Tel: 02 612 54865, Fax: 02 612 50740
http://nceph.anu.edu.au/Staff_Students/staff_pages/dear.php
CRICOS provider #00120C

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