Yes, they are all of the same length. -----Original Message----- From: Dimitri Liakhovitski [mailto:ld7...@gmail.com] Sent: Tuesday, April 21, 2009 8:32 AM To: Vemuri, Aparna Cc: r-help@r-project.org Subject: Re: [R] Fitting linear models
Are they of the same length? On Tue, Apr 21, 2009 at 11:31 AM, Vemuri, Aparna <avem...@epri.com> wrote: > The variables are all in separate vectors. > > -----Original Message----- > From: Dimitri Liakhovitski [mailto:ld7...@gmail.com] > Sent: Tuesday, April 21, 2009 8:26 AM > To: Vemuri, Aparna > Cc: David Winsemius; r-help@r-project.org > Subject: Re: [R] Fitting linear models > > Aparna, > > I should have been more explicit. Run ?lm . You'll see this: > > "lm(formula, data, subset, weights, na.action, > method = "qr", model = TRUE, x = FALSE, y = FALSE, qr = TRUE, > singular.ok = TRUE, contrasts = NULL, offset, ...)" > > So, in addition to specifying the formula, you have to specify the > data frame in which you keep your variables. I assume they are in a > data frame? (unless for some reasons you keep all variables as > separate vectors). > So, after you wrote the formula, you have to indicate the name of the > data frame, for example "MyData": > > model1<-lm(PBW~SO4+NO3+NH4, MyData) > > Dimitri > > On Tue, Apr 21, 2009 at 11:12 AM, Vemuri, Aparna <avem...@epri.com> wrote: >> David, >> Thanks for the suggestions. No, I did not label my dependent variable >> "function". >> >> My dependent variable PBW and all the independent variables are continuous >> variables. It is especially troubling since the order in which I input >> independent variables determines whether or not it gets a coefficient. Like >> I already mentioned, I checked the correlation matrix and picked the >> variables with moderate to high correlation with the independent variable. . >> So I guess it is not so naïve to expect a regression coefficient on all of >> them. >> >> Dimitri >> model1<-lm(PBW~SO4+NO3+NH4), gives me the same result as before. >> >> Bert: >> This is not homework. But I will remember to do my research before posting >> here. >> >> Aparna >> >> >> -----Original Message----- >> From: David Winsemius [mailto:dwinsem...@comcast.net] >> Sent: Monday, April 20, 2009 5:35 PM >> To: Vemuri, Aparna >> Cc: r-help@r-project.org >> Subject: Re: [R] Fitting linear models >> >> >> On Apr 20, 2009, at 7:26 PM, Vemuri, Aparna wrote: >> >>> I am not sure if this is an R-users question, but since most of you >>> here >>> are statisticians, I decided to give it a shot. >> >> You can omit the unnecessary preambles. >>> >>> >>> I am using the lm() function in R to fit a dependent variable to a set >>> of 3 to 5 independent variables. For this, I used the following >>> commands: >>> >>>> model1<-lm(function=PBW~SO4+NO3+NH4) >>> Coefficients: >>> (Intercept) SO4 NO3 NH4 >>> 0.01323 0.01968 0.01856 NA >>> >>> and >>> >>>> model2<-lm(function=PBW~SO4+NO3+NH4+Na+Cl) >>> >>> Coefficients: >>> (Intercept) SO4 NO3 NH4 >>> Na Cl >>> -0.0006987 -0.0119750 -0.0295042 0.0842989 0.1344751 >>> NA >>> >>> In both cases, the last independent variable has a coefficient of NA >>> in >>> the result. I say last variable because, when I change the order of >>> the >>> variables, the coefficient changes (see below). Can anyone point me to >>> the reason R behaves this way? Is there anyway for me to force R to >>> use >>> all the variables? I checked the correlation matrices to makes sure >>> there is no orthogonality between the variables. >> >> You really did not name your dependent variable "function" did you? >> Please stop that. >> >> Just a guess, ... since you have not provided enough information to do >> otherwise, ... Are all of those variables 1/0 dummy variables? If so >> and if you want to have an output that satisfies your need for >> labeling the coefficients as you naively anticipate, then put "0+" at >> the beginning of the formula or "-1" at the end, so that the intercept >> will disappear and then all variables will get labeled as you expect. >> >> -- >> David Winsemius, MD >> Heritage Laboratories >> 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. >> > > > > -- > Dimitri Liakhovitski > MarketTools, Inc. > dimitri.liakhovit...@markettools.com > -- Dimitri Liakhovitski MarketTools, Inc. dimitri.liakhovit...@markettools.com ______________________________________________ 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.
