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st: Re: RE: Data manipulation query


From   "Michael Blasnik" <michael.blasnik@verizon.net>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: RE: Data manipulation query
Date   Wed, 11 Jan 2006 19:36:10 -0500

I believe Nick's solution relies on there being only 2 possible scores per subject, but the second part of your query indicates that there may be multiple scores for a given year. Here's another approach:

starting with the 2nd question:
* first, drop missing scores if more than 1 score
bysort ID subject grade (score): drop if score==. & score[1]<.
* then drop lower scores when there's more than 1
bysort ID subject grade (score): drop if _n<_N

Now, assuming that grade only takes on the values of 4 and 6 and you've eliminated duplicates within ID subject grade (using the code above), the following will flag cases where there are grades for both cases within each ID and subject, and then you can drop the observations that don't meet that criterion:

bysort ID subject (grade): gen byte hasboth=score[1]<. & score[2]<.
drop if hasboth==0

Michael Blasnik
michael.blasnik@verizon.net


----- Original Message ----- From: "Nick Cox" <n.j.cox@durham.ac.uk>
To: <statalist@hsphsun2.harvard.edu>
Sent: Wednesday, January 11, 2006 6:58 PM
Subject: st: RE: Data manipulation query



(a)

Suppose you focus on English.

You can go

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

<snip>
(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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