How to loop over comparegoup function in R

Question

I have a large dataset and I want to apply comparegroups function in R. The dataset has number of grouping variables that I want to compare other variables on it; I wanted to loop over these grouping variables. the function is not accepting the loop

`vars <- c("fibrosis_stage", "Steatosis_stage", "patient_classification")
for (var in vars){
  model <- compareGroups(var~.,data = data)
  result.model <- createTable(model)
  export2xls(result.model,paste0(var,"comparisons.xlsx"))
}`

but I got the following error: Error in model.frame.default(formula = var ~ ., data = list(Gender = c(2L, : variable lengths differ

I tried even to make it in a function; with the grouping varaible as input but I had an error also.

Any one can help?