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st: vectored data

From   Kit Baum <>
Subject   st: vectored data
Date   Mon, 3 Oct 2005 09:46:23 -0400

Maarten said

forvalues i = 1/n {
gen vol`i' = length`i' * breadth`i' * height`i' * _pi / 6

The problem is that this measurement is performed a number of
times for each mouse on different days so that I'd need
breath1... etc.

gen volumem=lengthm*.....

What you are describing is a relational database in which the fixed characteristics of each mouse are stored in each table, with a mouse_id identifying them, and another table in which you have the time-varying measurements (perhaps weight of the mouse or how much it ate today), again identified with mouse_id and some kind of timestamp. In a RDBMS you would then join those two tables when you needed to juxtapose all of the characteristics. In Stata terms, that would suggest

mouse1.dta : mouse_id length breadth height birth_date blood_type

mouse2.dta: mouse_id timestamp weight amount_consumed

Then any time you want to combine the two tables you just merge them:

use mouse2
merge using mouse1, uniqusing

which appends the fixed characteristics to each record in the time- varying dataset.

See my FAQ about appending group characteristics to individual level data. This is essentially the same problem: for group read mouse and individual read mouse-measured-at-time-t.

Kit Baum, Boston College Economics

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