Is there a way of capturing variables in glm function in R? - r

Question

I would like to store indicator variables to be used in modelling into a vector to use them in a function. The goal is to use the created function to fit more than one model. I tried it as below but did not seem to get it right.
# Load data (from gtsummary package)
data(trial, package = "gtsummary")
# Specify the covariates
indicatorvars <- c("trt", "grade")
# Function
modelfunc <- function(outcome, covarates) {
glm({{outcome}} ~ {{covarates}},
data = trial, family = binomial)
}
modelfunc("response" , "indiatorvars")
# This one works
#glm(response ~ trt + grade, data = trial, family = binomial)

Answer 1

You can first build up your formula as a character string before converting it using as.formula. So the function would look like this:
modelfunc <- function(outcome, covarates) {
form <- paste(outcome, "~", paste(covarates, collapse = " + "))
glm(as.formula(form),
data = trial, family = binomial)
}
And here is your example:
modelfunc("response", indicatorvars)
#>
#> Call: glm(formula = as.formula(form), family = binomial, data = trial)
#>
#> Coefficients:
#> (Intercept) trtDrug B gradeII gradeIII
#> -0.87870 0.19435 -0.06473 0.08217
#>
#> Degrees of Freedom: 192 Total (i.e. Null); 189 Residual
#> (7 observations deleted due to missingness)
#> Null Deviance: 240.8
#> Residual Deviance: 240.3 AIC: 248.3
Created on 2021-04-27 by the reprex package (v2.0.0)
What I don't yet like about this solution is that the call is not very informative. So I would slightly adapt the function:
modelfunc <- function(outcome, covarates) {
form <- paste(outcome, "~", paste(covarates, collapse = " + "))
out <- glm(as.formula(form),
data = trial, family = binomial)
out$call <- out$formula # replace call with formula
out
}
modelfunc("response", indicatorvars)
#>
#> Call: response ~ trt + grade
#>
#> Coefficients:
#> (Intercept) trtDrug B gradeII gradeIII
#> -0.87870 0.19435 -0.06473 0.08217
#>
#> Degrees of Freedom: 192 Total (i.e. Null); 189 Residual
#> (7 observations deleted due to missingness)
#> Null Deviance: 240.8
#> Residual Deviance: 240.3 AIC: 248.3
Created on 2021-04-27 by the reprex package (v2.0.0)