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st: RE: RE: Data transformation


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: Data transformation
Date   Mon, 12 Nov 2007 12:29:13 -0000

I jumped to an incorrect reading of your problem through not reading it 
carefully enough. 

Point of curiosity: What about accidents involving 
three or more vehicles? Just not in the data? 

Point of technique: Keith's code was this 

bys Accidentnr: egen othersweight=sum(weight) 
bys Accidentnr: egen otherscost=sum(cost) 
replace othersweight=othersweight-weight 
replace otherscost=otherscost-cost 
rename weight ownweight 
rename cost owncost

namely: other value = sum of two values - this value 

Given that there are two, and only two, cars for
each accident, you can get there in this way too: 

bys Accidentnr : gen othersweight = weight[3 - _n] 
bys Accidentnr : gen otherscost = cost[3 - _n] 

The trick is simply a flip or reflection, exploiting
the fact under -by:- the subscript _n is determined 
within groups. Thus if _n is 1, 3 - _n is 2, and 
vice versa. 

Actually, if there is just one car in any accident, 
a call to observation 3 - _n will yield missing values, 
which is appropriate too.  

Lina Jonsson

I have a dataset concerning accidents involving two vehicles that I have
in two formats, wide and long like this:

long:

Accidentnr	vehiclenr	weight 	cost
1		0		1000		35000
1		1		1500		150000
2		0		1200		150000
2		1		1700		750000

wide:

Accidentnr	weight0	weight1	cost0		cost1
1		1000		1500		35000		150000
2		1200		1700		150000	750000

Now I whould like to transform the data to a long format but with
information also concering the other vehicle involved in each accident
like this:

Accidentnr	vehiclenr	ownweight 	othersweight	owncost
otherscost
1		0		1000		1500
35000		150000
1		1		1500		1000
150000	35000	
2		0		1200		1700
150000	750000
2		1		1700		1200
750000	150000

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