Hello,

This is a question motivated by curiosity, not a pressing problem. Any

responses are much appreciated! In the following code, function reg1 calls

glm with a formula object while reg2 uses a string. In both cases, glm

works; however, in the second case, the add1 function fails with the

following message: "Error in eval(predvars, data, env) : invalid 'envir'

argument." Any insight into what is going on "under the hood"?

Many thanks,

--Krishna

x1 = rnorm(100)

x2 = rnorm(100)

x3 = rnorm(100)

y = x1 + 2*x2 + 3*x3 + 0.05*rnorm(100)

d = data.frame(y,x1,x2,x3)

xset = paste("x",1:3,sep="")

reg1<-function(dep,cand,data){

f = paste(dep,"~1",sep="")

reg = glm(as.formula(f),family="gaussian",data)

add = add1(reg,cand,test="F")

}

reg2<-function(dep,cand,data){

f = paste(dep,"~1",sep="")

reg = glm(f,family="gaussian",data)

add = add1(reg,cand,test="F")

}

r1 = reg1("y",xset,d)

r2 = reg2("y",xset,d)

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