Coercing a list of variables in a function call
try the following:
model.it <- function (form, data, factor.id) {
if (!missing(factor.id) && all(factor.id %in% names(data)))
data[factor.id] <- lapply(data[factor.id], factor)
glm(form, data = data)
}
y <- c(1,2.1,3.3,4.3,5,6.5)
x1 <- c(1,1,1,2,2,2)
x2 <- c(1,2,3,1,2,3)
x3 <- c(1,3,2,4,2,4)
d <- data.frame(y, x1, x2, x3)
model.it(y ~ x1 + x2 + x3, d, c("x1", "x2"))
model.it(y ~ x1 + x2 + x3, d)
If you only plan to fit linear regression models, then it is advisable
that you lm() instead of glm(). I hope it helps.
Best,
Dimitris
Philip Whittall wrote:
This is hopefully a trivial problem for list subscribers, but I am very
new to writing R functions.
I wish to call an R function written by myself from another program to
fit a model. I need
to tell it which of the independent variables are factors. I need to do
this in a generic way,
so that when the list is passed, R will work through the variables in
the data frame and coerce them into being factors.
This is what I tried ...
# Fictitious data for illustration
y<-c(1,2.1,3.3,4.3,5,6.5)
x1<-c(1,1,1,2,2,2)
x2<-c(1,2,3,1,2,3)
x3<-c(1,3,2,4,2,4)
d<-as.data.frame(cbind(y,x1,x2,x3))
#Function definition
model_it=function(data=" ", model=" ", factors=list()){
attach(d) #Attach the data
formula<-as.formula(model) #Set up the model
#Identify the factors
if (length(factors)>0) for(i in 1:length(factors)){
factors[i]<-as.factor(factors[i])
}
#Fit the model
glm(formula, data=data)
}
#Function call attempted
model_it(data=d, model="y~x1+x2+x3", factors=list(x1,x2))
And this is the error message I received ...
Error in sort.list(unique.default(x), na.last = TRUE) :
'x' must be atomic for 'sort.list'
Have you called 'sort' on a list?
The line factors[i]<-as.factor(factors[i]) is the one responsible for
the error.
From the word 'atomic', my guess is that I have asked it to set each
value as a factor rather than the variable, but I don't know what syntax to use to get it to set the variable as a factor. Any suggestions gratefully appreciated. For the record, the above was run on windows XP using R2.8.0 This message should be regarded as confidential. If you have received this email in error please notify the sender and destroy it immediately. Statements of intent shall only become binding when confirmed in hard copy by an authorised signatory. The contents of this email may relate to dealings with other companies within the Detica Group plc group of companies. Detica Limited is registered in England under No: 1337451. Registered offices: Surrey Research Park, Guildford, Surrey, GU2 7YP, England. [[alternative HTML version deleted]]
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Dimitris Rizopoulos Assistant Professor Department of Biostatistics Erasmus Medical Center Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands Tel: +31/(0)10/7043478 Fax: +31/(0)10/7043014