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st: RE: i-1 in forvalues loop


From   Nick Cox <[email protected]>
To   "'[email protected]'" <[email protected]>
Subject   st: RE: i-1 in forvalues loop
Date   Tue, 18 Oct 2011 15:11:30 +0100

I don't understand what you are trying to do. I comment only on obvious Stata problems. 

`i-1' would only work if "i-1" were the name of a local macro, but it can't be such a name, as minus signs are not allowed in Stata names. 

gen bal`i' = bal`=`i'-1' * 3166.467

would at first sight work as then Stata knows to evaluate the expression 

`i' - 1 

on the fly. 

Your code largely consists of putting constants into variables, which is legal but not especially good style. 

Note that 

gen lotto=sum(studentsj3)                                                  //sum of target population

produces a _cumulative_ sum: only in the last observation will this be the actual sum, as your comment implies. Whether the comment or the code is what you want only you can say. 

Nick 
[email protected] 

Viktor Emonds

I am trying to draw a sample with random start, fixed interval systematic sampling procedure in each explicit stratum. The data in each stratum are already sorted by all the implicit stratifiers with serpentine sorting for a variable of particular interest. Now I just need to do the actual sampling and tried to start by doing the following:

use ethnicframe31                                                              //the specific explicit stratum
gen lotto=sum(studentsj3)                                                  //sum of target population
egen bal1= mean(3166.4667*runiform())                             //random starting point
forvalues i=2/15 {                                                          //Draw ' lotto balls' by adding the fixed interval
gen bal`i'= bal`i-1'*3166.4667
}

gen winnaar=0                                                                 //Identify ' winning'  schools
forvalues i=1/15{
replace winnaar=1 if inrange(bal`i',lotto[_n-1],lotto)
}

Apparently, the `i-1'  in the first loop is not understood. What am I doing wrong here? Thanks in advance!

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