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From |
"Michael Blasnik" <michael.blasnik@verizon.net> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: Re: Trouble with " if" |

Date |
Fri, 12 Mar 2004 09:29:41 -0500 |

Although it is easy to understand the misinterpretation, Stata is working according to its stated rules. The expression is evaluated left to right and therefore the first equality is evaluated first as a logical condition and the result of that condition (0 or 1) is then used to assess the second equality. Therefore 2==2==1 evaluates to true because 2==2 is true, which Stata assigns a value of 1 (it would be 0 if it were false) and then 1==1 is true. Parentheses might make it more clear: (2==2)==1 is more obviously true, but Stata does not require parentheses to follow it's rules concerning order of evaluation Michael Blasnik michael.blasnik@verizon.net ----- Original Message ----- From: "Christophe Bontemps" <bontemps@toulouse.inra.fr> To: <statalist@hsphsun2.harvard.edu> Sent: Friday, March 12, 2004 8:45 AM Subject: st: Trouble with " if" > Hi Everybody, > I find strange the way stata handle a double equality condition in "if" > statements > > Running the following trible loop on i, j and k with a condition like" if > `i'==`j'==`k' " gives a wrong answer, no warnings, no errors. > Of course i know the solution for this problem but why does Stata accept > these misleading statements in "if" ? > running on Stata 8 SE the following : > forvalues i = 1/3 { > forvalues j = 1/3 { > forvalues k = 1/3 { > display in yellow " i=`i' j=`j' k=`k' " > > if `i'==`j'==`k' { > di in green " case 1" > } > else { > di in red "case 2" > } > } > } > } > Gives > i=1 j=1 k=1 > case 1 > i=1 j=1 k=2 > case 2 > . > . > i=2 j=2 k=1 > case 1 > i=2 j=2 k=2 > case 2 > i=2 j=2 k=3 > . > . > i=3 j=3 k=1 > case 1 > i=3 j=3 k=2 > case 2 > i=3 j=3 k=3 > case 2 > > > Thanks > > * > * For searches and help try: > * http://www.stata.com/support/faqs/res/findit.html > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**Re: st: interaction with non-random treatment***From:*"Mark Schaffer" <M.E.Schaffer@hw.ac.uk>

**st: Trouble with " if"***From:*"Christophe Bontemps" <bontemps@toulouse.inra.fr>

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