how to loop over string variable in R

August 3, 2022

How to use the names in the string vector in models? for example why cant I do this

loop_variables = c("Age", "BMI", "Height")

for (i in 1:length(loop_variables){
    basic_logistic_model = glm(outcome~loop_variable[i], data=DB, family="binomial"
    summary(basic_logistic_model)
}

I see alot of R users doing vectors with names of study variables then looping it
what am I doing wrong?

>Solution :

It is the formula that needs to be update. We may use paste or reformulate. In addition, it is better to have an object to store the output of summary especially a list would suit.

summary_lst <- vector('list', length(loop_variables))
names(summary_lst) <- loop_variables
for (i in 1:length(loop_variables){
    # convert the column to factor column
    DB[[loop_variables[i]]] <- factor(DB[[loop_variables[i]]])
    # create the formula
    fmla <- reformulate(loop_variable[i], response = 'outcome')
    basic_logistic_model = glm(fmla, data=DB, family="binomial")
    # assign the summary output to the list element
    summary_lst[[i]] <- summary(basic_logistic_model)
}