Entering variables into regression function - r

Question

I have this feature_list that contains several possible values, say "A", "B", "C" etc. And there is time in time_list.
So I will have a loop where I will want to go through each of these different values and put it in a formula.
something like for(i in ...) and then my_feature <- feature_list[i] and my_time <- time_list[i].
Then I put the time and the chosen feature to a dataframe to be used for regression
feature_list<- c("GPRS")
time_list<-c("time")
calc<-0
feature_dim <- length(feature_list)
time_dim <- length(time_list)
data <- read.csv("data.csv", header = TRUE, sep = ";")
result <- matrix(nrow=0, ncol=5)
errors<-matrix(nrow=0, ncol=3)
for(i in 1:feature_dim) {
my_feature <- feature_list[i]
my_time <- time_list[i]
fitdata <- data.frame(data[my_feature], data[my_time])
for(j in 1:60) {
my_b <- 0.0001 * (2^j)
for(k in 1:60) {
my_c <- 0.0001 * (2^k)
cat("Feature: ", my_feature, "\t")
cat("b: ", my_b, "\t")
cat("c: ", my_c, "\n")
err <- try(nlsfit <- nls(GPRS ~ 53E5*exp(-1*b*exp(-1*c*time)), data=fitdata, start=list(b=my_b, c=my_c)), silent=TRUE)
calc<-calc+1
if(class(err) == "try-error") {
next
}
else {
coefs<-coef(nlsfit)
ess<-deviance(nlsfit)
result<-rbind(result, c(coefs[1], coefs[2], ess, my_b, my_c))
}
}
}
}
Now in the nls() call I want to be able to call my_feature instead of just "A" or "B" or something and then to the next one on the list. But I get an error there. What am I doing wrong?

Answer 1

You can use paste to create a string version of your formula including the variable name you want, then use either as.formula or formula functions to convert this to a formula to pass to nls.
as.formula(paste(my_feature, "~ 53E5*exp(-1*b*exp(-1*c*time))"))
Another option is to use the bquote function to insert the variable names into a function call, then eval the function call.

Answer 2

I worked with R a while ago, maybe you can give this a try:
What you want is create a formula with a list of variables right?
so if the response variable is the first element of your list and the others are the explanatory variables you could create your formula this way:
my_feature[0] ~ reduce("+",my_feature[1:]) . This might work.
this way you can create formulae that depends on the variables in my_features.