# Multiplication (PR#8466)

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## Multiplication (PR#8466)

 hi - in version 2.1 the command  >-2^2 gives -4 as the answer.  (-2)^2 is evaluated correctly. Cheers, George Casella -- George Casella                   Phone: (352) 392-1941 Ext. 204 Distinguished Professor and Chair Cell:  (352) 682-7210 Department of Statistics   Fax:   (352) 392-5175 University of Florida           Email: [hidden email] P.O. Box 118545 Gainesville, FL 32611-8545 ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 On Fri, 6 Jan 2006, [hidden email] wrote: > hi - in version 2.1 the command > > >-2^2 > > gives > > -4 > > as the answer.  (-2)^2 is evaluated correctly. So is -2^2.  The precedence of ^ is higher than that of unary minus. It may be surprising, but it *is* documented and has been in S for a long time.   -thomas Thomas Lumley Assoc. Professor, Biostatistics [hidden email] University of Washington, Seattle ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 On 1/6/06, Thomas Lumley <[hidden email]> wrote: > On Fri, 6 Jan 2006, [hidden email] wrote: > > > hi - in version 2.1 the command > > > > >-2^2 > > > > gives > > > > -4 > > > > as the answer.  (-2)^2 is evaluated correctly. > > So is -2^2.  The precedence of ^ is higher than that of unary minus. It > may be surprising, but it *is* documented and has been in S for a long > time. See ?Syntax ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 In reply to this post by casella On 1/6/06, Thomas Lumley <[hidden email]> wrote: > On Fri, 6 Jan 2006, [hidden email] wrote: > > > hi - in version 2.1 the command > > > > >-2^2 > > > > gives > > > > -4 > > > > as the answer.  (-2)^2 is evaluated correctly. > > So is -2^2.  The precedence of ^ is higher than that of unary minus. It > may be surprising, but it *is* documented and has been in S for a long > time. See ?Syntax ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 How do people even notice stuff like this.  You would never hard-coding (-2)^2 or -2^2 anyway. The part being squared would be a variable, in which case it works correctly: > a<- -2 > a [1] -2 > a^2 [1] 4 Sometimes it seems that people go looking for bugs... and therefore see bugs all around them. On 1/6/06, [hidden email] <[hidden email]> wrote: > > On 1/6/06, Thomas Lumley <[hidden email]> wrote: > > On Fri, 6 Jan 2006, [hidden email] wrote: > > > > > hi - in version 2.1 the command > > > > > > >-2^2 > > > > > > gives > > > > > > -4 > > > > > > as the answer.  (-2)^2 is evaluated correctly. > > > > So is -2^2.  The precedence of ^ is higher than that of unary minus. It > > may be surprising, but it *is* documented and has been in S for a long > > time. > > See ?Syntax > > ______________________________________________ > [hidden email] mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel>         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 Precedence rules are tricky, in general, and the usual advice with most programming languages is to liberally use parentheses when in doubt.  Its actually not that surprising in this case but consider 0-1:3 and -1:3 which give different results since one uses binary minus and the other uses unary minus and the order of precedence from highest to lowest is unary minus, : and binary minus.  If one used parentheses in these cases it would be clear even without detailed knowledge of the precedence rules (which likely no one can remember anyways). On 1/6/06, roger bos <[hidden email]> wrote: > How do people even notice stuff like this.  You would never hard-coding > (-2)^2 or -2^2 anyway. The part being squared would be a variable, in which > case it works correctly: > > > a<- -2 > > a > [1] -2 > > a^2 > [1] 4 > > Sometimes it seems that people go looking for bugs... and therefore see bugs > all around them. > > On 1/6/06, [hidden email] <[hidden email]> wrote: > > > > On 1/6/06, Thomas Lumley <[hidden email]> wrote: > > > On Fri, 6 Jan 2006, [hidden email] wrote: > > > > > > > hi - in version 2.1 the command > > > > > > > > >-2^2 > > > > > > > > gives > > > > > > > > -4 > > > > > > > > as the answer.  (-2)^2 is evaluated correctly. > > > > > > So is -2^2.  The precedence of ^ is higher than that of unary minus. It > > > may be surprising, but it *is* documented and has been in S for a long > > > time. > > > > See ?Syntax > > > > ______________________________________________ > > [hidden email] mailing list > > https://stat.ethz.ch/mailman/listinfo/r-devel> > > >        [[alternative HTML version deleted]] > > ______________________________________________ > [hidden email] mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel> ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 In reply to this post by Thomas Lumley Thomas Lumley <[hidden email]> writes: > On Fri, 6 Jan 2006, [hidden email] wrote: > > > hi - in version 2.1 the command > > > > >-2^2 > > > > gives > > > > -4 > > > > as the answer.  (-2)^2 is evaluated correctly. > > So is -2^2.  The precedence of ^ is higher than that of unary minus. It > may be surprising, but it *is* documented and has been in S for a long > time. Pretty much standard too, for languages that have an exponentiation operator. AFAICS Fortran, Perl, SAS all have ** at higher precedence than unary minus (or equal, but evaluate right to left). Stata seems like it might be the exception. --    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K  (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918 ~~~~~~~~~~ - ([hidden email])                  FAX: (+45) 35327907 ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 In reply to this post by casella Thomas Lumley <[hidden email]> writes: > On Fri, 6 Jan 2006, [hidden email] wrote: > > > hi - in version 2.1 the command > > > > >-2^2 > > > > gives > > > > -4 > > > > as the answer.  (-2)^2 is evaluated correctly. > > So is -2^2.  The precedence of ^ is higher than that of unary minus. It > may be surprising, but it *is* documented and has been in S for a long > time. Pretty much standard too, for languages that have an exponentiation operator. AFAICS Fortran, Perl, SAS all have ** at higher precedence than unary minus (or equal, but evaluate right to left). Stata seems like it might be the exception. --    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K  (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918 ~~~~~~~~~~ - ([hidden email])                  FAX: (+45) 35327907 ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 In reply to this post by casella While we're swapping precedence tales, can you guess what this gives: > q <- TRUE > 2 + !q + 3 It's "2", not "5".  Bit me in the arse just the other day :-) -- David Brahm ([hidden email]) ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 In reply to this post by Thomas Lumley Thomas Lumley wrote: >On Fri, 6 Jan 2006, [hidden email] wrote: > >   > >>hi - in version 2.1 the command >> >>     >> >>>-2^2 >>>       >>> >>gives >> >>-4 >> >>as the answer.  (-2)^2 is evaluated correctly. >>     >> > >So is -2^2.  The precedence of ^ is higher than that of unary minus. It >may be surprising, but it *is* documented and has been in S for a long >time. > > > -thomas >   > No, it's not surprising. At least to me... In the country where I grew up, I've been teached that -x^2 means -(x^2) not (-x)^2 ;-) H. -- ------------------------ Hervé Pagès E-mail: [hidden email]  Phone: (206) 667-5791    Fax: (206) 667-1319 ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
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## Re: Multiplication (PR#8466)

 In reply to this post by casella Thomas Lumley wrote: >On Fri, 6 Jan 2006, [hidden email] wrote: > >   > >>hi - in version 2.1 the command >> >>     >> >>>-2^2 >>>       >>> >>gives >> >>-4 >> >>as the answer.  (-2)^2 is evaluated correctly. >>     >> > >So is -2^2.  The precedence of ^ is higher than that of unary minus. It >may be surprising, but it *is* documented and has been in S for a long >time. > > > -thomas >   > No, it's not surprising. At least to me... In the country where I grew up, I've been teached that -x^2 means -(x^2) not (-x)^2 ;-) H. -- ------------------------ Hervé Pagès E-mail: [hidden email]  Phone: (206) 667-5791    Fax: (206) 667-1319 ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel