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st: RE: strange foreach loop result


From   Matthew Watt <matthew.watt@msci.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: strange foreach loop result
Date   Wed, 15 Dec 2010 11:53:02 -0500

David,
Do you get the same results if you use an "if/else if" structure instead of a pure if structure?  As you have it now, each of your loop's tests is independent of the previous tests, meaning that even if `var' == slope, you test to see if `var' also equals lower, upper, and ed50.  The result of this is that if `var' equals both slope and ed50, you will assign a value of 4 to slope.  If you use an if/else structure, the else clause will only be tested if the "if" clause is false.

Of course, you may end up with ed50 having a value of 1 if ed50 and slope are equal, should you use if/else.

--Matt

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Airey, David C
Sent: Wednesday, December 15, 2010 11:40 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: strange foreach loop result

.

I'm getting a really strange foreach loop result I don't understand.

In the first code snippet on fictitious data, I get what I want. In the second code snippit on the real data I get a strange result for when the condition:

if `var' == slope local myvar 1

is evaluated when `var' is slope. It produces the result myvar==4, when it should return myvar==1.

Anyone have a clue where my error is?


clear
set obs 10
gen a = 1
gen b = 2
gen c = 3
gen d = 4
foreach var of varlist a b c d {
        if `var' == a local myvar 1
        if `var' == b local myvar 2
        if `var' == c local myvar 3
        if `var' == d local myvar 4
        display "`var'", "`myvar'"
}

produces:

a 1
b 2
c 3
d 4


use result_pilot.dta, clear
keep slope lower upper ed50
foreach var of varlist slope lower upper ed50 {
        if `var' == slope local myvar 1
        if `var' == lower local myvar 2
        if `var' == upper local myvar 3
        if `var' == ed50 local myvar 4
        display "`var'", "`myvar'"
}

produces:

slope 4 <--weird, should be slope 1
lower 2
upper 3
ed50 4


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