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st: RE: if/else command


From   "David Harrison" <[email protected]>
To   <[email protected]>
Subject   st: RE: if/else command
Date   Thu, 6 Jan 2005 15:08:44 -0000

The programming function

if <exp> {
	<code>
}

evaluates a _single_ logical expression <exp> and executes <code> if it is true, it does not evaluate <exp> on individual observations.

In your example, with <exp> being certification==1, the variable certification is only being evaluated on the first observation in your data (equivalent to certification[1]==1). To get what you want, you would need to program

replace age = 22 if age <= 5 & certification==1
replace age = 30 if age >= 6 & age <= 15 & certification==1
etc

Alternatively, you could do this in fewer steps with the command -recode-.

David
[email protected]

-----Original Message-----
From: Anek Stata [mailto:[email protected]]
Sent: 06 January 2005 14:54
To: [email protected]
Cc: [email protected]
Subject: st: if/else command


Greetings everyone,

I am using Stata 8.1 on Win2000. My data set contains variable 
"certification", which takes values 1 or 2 only. I am trying to group 
respondents from these two "certification" sets into age groups. For SOME 
REASON, the if command for certification==1 executes all the replace 
commands, but when it goes to the second if, none of the replace commands 
within the curly brackets get executed.

Below is the code I am using:
----------------------------------------

if certification == 1 { ;
replace age = 22 if age <= 5;
replace age = 30 if age >= 6 & age <= 15;
replace age = 40 if age >= 16 & age <= 20;
replace age = 50 if age > 20;
{ ;
else if certification == 2 { ;
replace age = 22 if age <= 3;
replace age = 30 if age >= 4 & age <= 13;
replace age = 40 if age >= 14 & age <= 24;
replace age = 50 if age == 25;
replace age = 50 if age == 26;
replace age = 50 if age == 27;
replace age = 50 if age == 28;
};

----------------
I have tried to break it on purpose, writing "if certification==3". This 
gives me NO ERRORS, even though there is never a value 3 in variable 
certification. This is obviously wrong. I have also tried the code with and 
without "else" (just trying to execute another if), to no avail. I've tried:

...
replace age = 50 if age > 20;
};
else{;
replace age = 22 if age <= 3;
...

and

...
replace age = 50 if age > 20;
};
if certification==2{;
replace age = 22 if age <= 3;
...


Since the help file is USELESS, I'd like to ask for your help, if you can 
spot what I am doing wrong.

Thanks a lot,
Ane

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