[R] a question regarding updating formulas with coefficients
I have formulae with coefficents that I would like to update. However, I get some strange results. For example, see the following: For the formula y ~ d+ 3*r+t I want to add a variable p, so update(y~d+0*r+t, .~.+p) produces y ~ d + t + p - 1 If the coefficient is not 0, but rather, something else - say, 3, I get the following: update(y~d+3*r+t, .~.+p) Error in terms.formula(tmp, simplify = TRUE) : invalid model formula in ExtractVars Is there a way to do this, or a different call I should be trying? -Jarrett __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] a question regarding updating formulas with coefficients
On Aug 11, 2010, at 6:03 PM, Jarrett Byrnes wrote: I have formulae with coefficents that I would like to update. However, I get some strange results. For example, see the following: For the formula y ~ d+ 3*r+t Did you really get meaningful results from that formula? Care to provide an example? Maybe there is something more for me to learn. I want to add a variable p, so update(y~d+0*r+t, .~.+p) In formulas the * operator is an interaction creator. so you told R to make 0 + r + 0:r. Probably not what you thought you were doing. So what were you trying to do anyway? produces y ~ d + t + p - 1 Which at least explains why you got the -1 (which in R formulas is that same as +0). If the coefficient is not 0, but rather, something else - say, 3, What do you think you are accomplishing when you put a scalar coefficient in the formula? I get the following: update(y~d+3*r+t, .~.+p) Error in terms.formula(tmp, simplify = TRUE) : invalid model formula in ExtractVars Is there a way to do this, or a different call I should be trying? What you should be doing depends on what you want to happen. -- David Winsemius, MD West Hartford, CT __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] a question regarding updating formulas with coefficients
On Wed, 11 Aug 2010, David Winsemius wrote: On Aug 11, 2010, at 6:03 PM, Jarrett Byrnes wrote: I have formulae with coefficents that I would like to update. However, I get some strange results. For example, see the following: For the formula y ~ d+ 3*r+t Did you really get meaningful results from that formula? Care to provide an example? Maybe there is something more for me to learn. I want to add a variable p, so update(y~d+0*r+t, .~.+p) In formulas the * operator is an interaction creator. so you told R to make 0 + r + 0:r. Probably not what you thought you were doing. So what were you trying to do anyway? produces y ~ d + t + p - 1 Which at least explains why you got the -1 (which in R formulas is that same as +0). If the coefficient is not 0, but rather, something else - say, 3, What do you think you are accomplishing when you put a scalar coefficient in the formula? Maybe he wants ?I ?? Chuck I get the following: update(y~d+3*r+t, .~.+p) Error in terms.formula(tmp, simplify = TRUE) : invalid model formula in ExtractVars Is there a way to do this, or a different call I should be trying? What you should be doing depends on what you want to happen. -- David Winsemius, MD West Hartford, CT __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Charles C. Berry(858) 534-2098 Dept of Family/Preventive Medicine E mailto:cbe...@tajo.ucsd.edu UC San Diego http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901 __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] a question regarding updating formulas with coefficients
On Aug 11, 2010, at 6:45 PM, Charles C. Berry wrote: On Wed, 11 Aug 2010, David Winsemius wrote: On Aug 11, 2010, at 6:03 PM, Jarrett Byrnes wrote: I have formulae with coefficents that I would like to update. However, I get some strange results. For example, see the following: For the formula y ~ d+ 3*r+t Did you really get meaningful results from that formula? Care to provide an example? Maybe there is something more for me to learn. I want to add a variable p, so update(y~d+0*r+t, .~.+p) In formulas the * operator is an interaction creator. so you told R to make 0 + r + 0:r. Probably not what you thought you were doing. So what were you trying to do anyway? produces y ~ d + t + p - 1 Which at least explains why you got the -1 (which in R formulas is that same as +0). If the coefficient is not 0, but rather, something else - say, 3, What do you think you are accomplishing when you put a scalar coefficient in the formula? Maybe he wants ?I Possibly, but wouldn't that just result in a deflation by a factor of 3 of the estimated coefficient if you wrappedI around that rem ... I(3*r) ? I also wondered if he might need to be referred to: ?offset ?? ?? back 'atcha. -- David. Chuck I get the following: update(y~d+3*r+t, .~.+p) Error in terms.formula(tmp, simplify = TRUE) : invalid model formula in ExtractVars Is there a way to do this, or a different call I should be trying? What you should be doing depends on what you want to happen. -- David David Winsemius, MD West Hartford, CT __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] a question regarding updating formulas with coefficients
On Wed, 11 Aug 2010, David Winsemius wrote: On Aug 11, 2010, at 6:45 PM, Charles C. Berry wrote: On Wed, 11 Aug 2010, David Winsemius wrote: On Aug 11, 2010, at 6:03 PM, Jarrett Byrnes wrote: I have formulae with coefficents that I would like to update. However, I get some strange results. For example, see the following: For the formula y ~ d+ 3*r+t Did you really get meaningful results from that formula? Care to provide an example? Maybe there is something more for me to learn. I want to add a variable p, so update(y~d+0*r+t, .~.+p) In formulas the * operator is an interaction creator. so you told R to make 0 + r + 0:r. Probably not what you thought you were doing. So what were you trying to do anyway? produces y ~ d + t + p - 1 Which at least explains why you got the -1 (which in R formulas is that same as +0). If the coefficient is not 0, but rather, something else - say, 3, What do you think you are accomplishing when you put a scalar coefficient in the formula? Maybe he wants ?I Possibly, but wouldn't that just result in a deflation by a factor of 3 of the estimated coefficient if you wrappedI around that rem ... I(3*r) ? Quite so. It is just one way (and I am not touting it) of rescaling a variable. I also wondered if he might need to be referred to: ?offset ?? ?? back 'atcha. My '??' was intended for the OP, but your guess seems good to me. Chuck -- David. Chuck I get the following: update(y~d+3*r+t, .~.+p) Error in terms.formula(tmp, simplify = TRUE) : invalid model formula in ExtractVars Is there a way to do this, or a different call I should be trying? What you should be doing depends on what you want to happen. -- David David Winsemius, MD West Hartford, CT __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Charles C. Berry(858) 534-2098 Dept of Family/Preventive Medicine E mailto:cbe...@tajo.ucsd.edu UC San Diego http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901 __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
