[R] summing columns of data frame by group

I have a data frame and one separate vector that is a grouping variable for the data frame. I would like to take all rows of the data frame belonging to each group and then sum the columns with out using a for statement. Something like: take all rows of group 1 then apply(group1.data,1,sum),

[R] multicollinearity in nlme models

I am working on a nlme model that has multiple fixed effects (linear and nonlinear) with a nonlinear (asymptotic) random effect. asymporig-function(x,th1,th2)th1*(1-exp(-exp(th2)*x)) asymporigb-function(x,th1b,th2b)th1b*(1-exp(-exp(th2b)*x))

[R] correlation structure

I have been using a nlme model and wish to specify the correlation structure. My data is grouped (bas), but I have no time component or adequate spatial description beyond the grouping variable. So I chose the simplest structure and updated my original nlme model by: update(model,

[R] nlme correlated random effects

I am examining the following nlme model. asymporig-function(x,th1,th2)th1*(1-exp(-exp(th2)*x)) mod1-nlme(fa20~(ah*habdiv+ad*log(d)+ads*ds+ads2*ds2+at*trout)+asymporig(da.p,th1,th2), fixed=ah+ad+ads+ads2+at+th1+th2~1, random=th1+th2~1,

[R] nlme model

I am having trouble figuring out the right form for the nlme arguments. I do have examples in Modern and Applied Statistics with S and from other sources, but I still can't figure it out. I am trying to estimate species richness (sr) in streams across minnesota. My predictor variables are

[R] installing packages and windows vista

I installed R (R-2.4.1-win32.exe) on a new computer with Windows Vista and a 64 bit operating system (hp dv9000 with intel core t7200). The base R runs fine, but I can not get any of the packages to load. From within R I choose install packages choose a site then a package. I tried installing