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st: RE: Data manipulation query


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Data manipulation query
Date   Wed, 11 Jan 2006 23:58:37 -0000

(a) 

Suppose you focus on English. 

You can go

egen nEnglish = sum(strpos(subject, "English")), by(ID) 
keep if nEnglish == 2 
drop nEnglish 

Or suppose you focus on Mathematics. 

You can go

egen nMath = sum(strpos(subject,"Math")), by(ID) 
keep if nMath == 2 
drop nMath

(b) 

Given (a), 

bysort ID (Math) : gen max = score[2] 

etc. 

Nick 
n.j.cox@durham.ac.uk 

Anirudh V. S. Ruhil, Ph.D. wrote 
 
> I have two data manipulation questions:
> 
> (a) Lets says I have a dataset of students' scores for 2 
> subjects when 
> tested in the 4th grade, and their scores on similar tests 
> taken in the 6th 
> grade. Some students are lost between the 4th and 6th grade 
> but some show 
> up in both grades. The data structure is as follows ...
> 
> ID 	grade 	subject	 	score
> A1	04 		English	 	271
> A1	04		Mathematics	190
> A1	06		English	 	260
> A1	06		Mathematics	214
> A2	04		English		.
> A2	04 		Mathematics	165
> A2	06		English		187
> A2	06		Mathematics	193
> A3	04		English		.
> A3	04		Mathematics	.
> A3	06		English		216
> A3	06		Mathematics	265
> 
> How would I create a subset of these data such that the subset only 
> contains records for students with non-missing scores in a 
> given subject on 
> BOTH the 4th and the 6th grade tests?
> 
> (b) In the same dataset, let us assume there are multiple 
> records for some 
> students on a single grade and subject. For example,
> 
> A4	04		English		191
> A4	04		English		219
> 
> Of these multiple records, how can I select entries with the 
> HIGHER SCORE? 
> (i.e., the lower scores have to be discarded).
> 
> I'm sure there is a quickfire way to solve both so I'd be grateful if 
> someone points me in the right direction in STATAspeak (9.1).
> 

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