Great! Have managed to shift my dataset to positive. Thanks for all your help. Henry.
2009/11/30 David Winsemius <dwinsem...@comcast.net> > > On Nov 30, 2009, at 11:47 AM, Henry Thorogood wrote: > > The scale function seems to have tackled the skew, just looking at the >> boxplots for the data. >> >> The boxcox function I'm using is boxcox(), from MASS. >> > > I'm puzzled. When I look at the boxcox function in MASS it says: > > "Arguments > object a formula or fitted model object. Currently only lm and aov > objects are handled." > > And I did not see anything about a regression model in what you wrote. > > > I've looked through >> the help page, but I don't think (from what I can see) there's a way to >> make >> the boxcox function handle the negative values, unlike say the b.c >> function >> (from car, I think), which has a 'start' argument. >> > > That was the package I was thinking you might be using. > > >> How would I add, say, a constant c to each piece of data? Whilst I think I >> understand the stats, I'm pretty terrible at manipulating R, as I've only >> been using it for a few days! >> > > if the object is "obj" then adding a constant, "ccc", is as simple as: > > shift_obj <- obj + ccc > > You really should go back to your introductory text now and be more > systematic in pursuit of learning the language . This is extremely basic > stuff so you are probably not at the stage to be learning by > experimentation. Get the basics first. > > (Notice that I don't use "c" as the name of an object. It is a crucial > function in R and you will tie your brain in knots if you have both meanings > of "c" floating around.) > > >> Thanks again, >> >> Henry >> >> 2009/11/30 David Winsemius <dwinsem...@comcast.net> >> >> >>> On Nov 30, 2009, at 11:02 AM, Henry Thorogood wrote: >>> >>> Hi, >>> >>>> >>>> I'm doing some work with linear models, and I've scaled my data using >>>> the >>>> scale(dataset) function. This was great at removing the skew, but I now >>>> can't perform the Box Cox transformation on the data set (using the >>>> boxcox(dataset) function), as the scaling has returned negative values. >>>> >>>> >>> Scaling (at least that using the default approach with that function) >>> should not "remove" skewness. >>> >>> >>> >>> So my question is: how can I get the scale function to return a positive >>>> set >>>> of data (so I can use Box-Cox), >>>> >>>> >>> You could shift the scaled values to the right. >>> >>> >>> or how can I get the boxcox function to >>> >>>> handle negative values. >>>> >>>> >>> Which boxcox function? And have you looked at all of its available >>> parameters? >>> >>> -- >>> David Winsemius, MD >>> Heritage Laboratories >>> West Hartford, CT >>> >>> >>> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> 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. >> > > David Winsemius, MD > Heritage Laboratories > West Hartford, CT > > [[alternative HTML version deleted]] ______________________________________________ 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.
