I need to call the mlogit() R function from inside another function.
This is a function for demonstrative purposes:
#-------------------------
# DEMO FUNCTION
#-------------------------
# f = formula (string)
# fData = data.frame
# cVar = choice variable (string)
# optVar = alternative variable (string)
##########################
mlogitSum <- function(f, fData, cVar="choice", optVar="option"){
library(mlogit)
r2 <- mlogit(as.formula(f), shape = "long", data = fData, alt.var=optVar, choice = cVar)
return(summary(r2))
}
Apparently there is an environment problem, so that variables not declared globally are not found by the mlogit() function as arguments.
This example doesn't work:
mydata <- read.csv(url("http://www.ats.ucla.edu/stat/r/dae/mlogit.csv"))
attach(mydata)
library(mlogit)
mydata$brand<-as.factor(mydata$brand)
mlData<-mlogit.data(mydata, varying=NULL, choice="brand", shape="wide")
myFormula <-"brand~1|female+age"
var1 <- "brand"
var2 <- "alt"
mlogitSum(myFormula, fData = mlData, var1, var2)
While if the variables are assigned in the main environment it works:
mydata <- read.csv(url("http://www.ats.ucla.edu/stat/r/dae/mlogit.csv"))
attach(mydata)
library(mlogit)
mydata$brand<-as.factor(mydata$brand)
fData<-mlogit.data(mydata, varying=NULL, choice="brand", shape="wide")
myFormula <-"brand~1|female+age"
cVar <- "brand"
optVar <- "alt"
mlogitSum(myFormula, fData, cVar, optVar)
Alternatively it works if I assign the variables globally from inside the function
#-------------------------
# DEMO FUNCTION
#-------------------------
# f = formula (string)
# fData = data.frame
# cVar = choice variable (string)
# optVar = alternative variable (string)
##########################
mlogitSum_rev <- function(f, fData, cVar="choice", optVar="option"){
fData<<-fData
cVar<<-cVar
optVar<<-optVar
#return(head(lcmData))
library(mlogit)
#mi serve per poi estrarre model.matrix(r2), per il resto sarebbe ridondante
r2 <- mlogit(as.formula(f), shape = "long", data = fData, alt.var=optVar, choice = cVar)
return(summary(r2))
}
mydata <- read.csv(url("http://www.ats.ucla.edu/stat/r/dae/mlogit.csv"))
attach(mydata)
library(mlogit)
mydata$brand<-as.factor(mydata$brand)
mlData<-mlogit.data(mydata, varying=NULL, choice="brand", shape="wide")
myFormula <-"brand~1|female+age"
var1 <- "brand"
var2 <- "alt"
mlogitSum_rev(myFormula, mlData, var1, var2)
Any idea on how to avoid to assign the variables globally?
