Iterating and looping over multiple columns in glm in r using a name from another variable-CodePudding

I am trying to iterate over multiple columns for a glm function in R.

view(mtcars)
names <- names(mtcars[-c(1,2)])

for(i in 1:length(names)){
  
  print(paste0("Starting iterations for ",names[i]))
  
  
  model <-  glm(mpg ~ cyl   paste0(names[i]), data=mtcars, family = gaussian())
  summary(model)
  
  print(paste0("Iterations for ",names[i], " finished"))
}

however, I am getting the following error:

[1] "Starting iterations for disp"
Error in model.frame.default(formula = mpg ~ cyl   paste0(names[i]), data = mtcars,  : 
  variable lengths differ (found for 'paste0(names[i])')

Not sure, how I can correct this.

CodePudding user response：

mpg ~ cyl paste0(names[i]) or even mpg ~ cyl names[i] is not a valid syntax for a formula. Use

reformulate(c("cyl", names[i]), "mpg")

instead, which dynamically creates a formula from variable names.

CodePudding user response：

Since you need to build your model formula dynamically from string you need as.formula. Alternatively, consider reformulate which receives response and RHS variable names:

...
    fml <- reformulate(c("cyl", names[i]), "mpg")
    model <-  glm(fml, data=mtcars, family = gaussian())
    summary(model)
...

CodePudding user response：

glm takes a formula which you can create using as.formula()

predictors <- names(mtcars[-c(1,2)])

for(predictor in predictors){
  
  print(paste0("Starting iterations for ",predictor))
  
  model <-  glm(as.formula(paste0("mpg ~ cyl   ",predictor)), 
                           data=mtcars, 
                           family = gaussian())
  print(summary(model))
  
  print(paste0("Iterations for ",predictor, " finished"))
}