There must be a simple answer. I want to plot an expression, where the expression is held in a string variable. The "obvious" solution along the lines of ex<-"x^2" plot( c(0,1), c(0,1), main=as.expression(ex) ) gives me the a title x^2 - ie doesn't treat it like an expression. I suspect I don't understand expressions properly. For the real problem I do need to have my expression string in a variable as it is data-dependent. Can someone tell me the magic words? Steve Dr Steve Roberts steve.roberts at man.ac.uk Senior Lecturer in Medical Statistics, CMMCH NHS Trust and University of Manchester Biostatistics Group, 0161 275 5192 / 0161 276 5785
You *parse* strings to form expressions. plot( c(0,1), c(0,1), main=parse(text=ex) ) On Thu, 10 Jun 2004, Steve Roberts wrote:> There must be a simple answer. I want to plot an expression, > where the expression is held in a string variable. The "obvious" > solution along the lines of > > ex<-"x^2" > plot( c(0,1), c(0,1), main=as.expression(ex) ) > > gives me the a title x^2 - ie doesn't treat it like an expression. I > suspect I don't understand expressions properly. For the real > problem I do need to have my expression string in a variable as it is > data-dependent.You might also want to explore substitute.> Can someone tell me the magic words?-- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
Hi On 10 Jun 2004 at 12:28, Steve Roberts wrote:> There must be a simple answer. I want to plot an expression, > where the expression is held in a string variable. The "obvious" > solution along the lines of > > ex<-"x^2" > plot( c(0,1), c(0,1), main=as.expression(ex) )Plotmath example led me to ex<-expression(x^2) plot( c(0,1), c(0,1), main=(ex) ) hope it is what you want. Cheers Petr> > gives me the a title x^2 - ie doesn't treat it like an expression. I > suspect I don't understand expressions properly. For the real problem > I do need to have my expression string in a variable as it is > data-dependent. > > Can someone tell me the magic words? > > Steve > Dr Steve Roberts > steve.roberts at man.ac.uk > > Senior Lecturer in Medical Statistics, > CMMCH NHS Trust and University of Manchester Biostatistics Group, 0161 > 275 5192 / 0161 276 5785 > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.htmlPetr Pikal petr.pikal at precheza.cz
No that isn't it I'm afraid - my expression is pasted together from various bits and pieces and is at some stage a string variable. I needed parse as Brian pointed out.... Thanks anyway, Steve. From: "Petr Pikal" <petr.pikal at precheza.cz> To: "Steve Roberts" <steve.roberts at man.ac.uk> Date sent: Thu, 10 Jun 2004 13:44:21 +0200 Subject: Re: [R] Help with plotmath Copies to: r-help at stat.math.ethz.ch Priority: normal> Hi > > On 10 Jun 2004 at 12:28, Steve Roberts wrote: > > > There must be a simple answer. I want to plot an expression, > > where the expression is held in a string variable. The "obvious" > > solution along the lines of > > > > ex<-"x^2" > > plot( c(0,1), c(0,1), main=as.expression(ex) ) > > Plotmath example led me to > > ex<-expression(x^2) > plot( c(0,1), c(0,1), main=(ex) ) > > hope it is what you want. > > Cheers > Petr > > > > > > gives me the a title x^2 - ie doesn't treat it like an expression. I > > suspect I don't understand expressions properly. For the real problem > > I do need to have my expression string in a variable as it is > > data-dependent. > > > > Can someone tell me the magic words? > > > > Steve > > Dr Steve Roberts > > steve.roberts at man.ac.uk > > > > Senior Lecturer in Medical Statistics, > > CMMCH NHS Trust and University of Manchester Biostatistics Group, 0161 > > 275 5192 / 0161 276 5785 > > > > ______________________________________________ > > R-help at stat.math.ethz.ch mailing list > > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide! > > http://www.R-project.org/posting-guide.html > > Petr Pikal > petr.pikal at precheza.cz > >Dr Steve Roberts steve.roberts at man.ac.uk Senior Lecturer in Medical Statistics, CMMCH NHS Trust and University of Manchester Biostatistics Group, 0161 275 5192 / 0161 276 5785