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st: RE: RE: if "macro" == value {

From   "Nick Cox" <[email protected]>
To   <[email protected]>
Subject   st: RE: RE: if "macro" == value {
Date   Tue, 3 Feb 2004 10:37:18 -0000

James Harris posted this code. 

foreach ICD in i21 {
	foreach age in 25 35 45 {
		foreach sex in m f {
			local deaths = "`ICD'_`age'`sex'" 
			local population = "pop`age'`sex'"
			macro list
			list year `ICD'_`age'`sex' pop`age'`sex' `deaths' `population'
			poisson `deaths' year, exposure (`population')

Phil Ryan answered the associated question. I just want 
to comment on one detail. 

In the macro assignment

local deaths = "`ICD'_`age'`sex'" 

what you're doing is just asking Stata to insert strings 
in appropriate places; there is no use of string 
functions or operators. In such cases the = sign 
is not necessary and you can just go 

local deaths "`ICD'_`age'`sex'" 

Going further: there is a positive benefit 
to doing this when you are dealing with very 
long strings. It is not pertinent here, as the 
string concerned is a variable name, but there 
is a limit to string expression lengths which can be handled
(it varies: see help on -limits-). In other problems
this can lead to bizarre bugs when long strings are 

In short,  

local deaths = "`ICD'_`age'`sex'" 
local deaths "`ICD'_`age'`sex'" 

are not exactly equivalent. It is a better habit 
to use the second form. (As said, this hinges 
on not using here any string operators or functions.) 

[email protected] 


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