Problem using function with "as.formula" in a loop in R - r

Question

I've created a function that returns an ANOVA table, and it uses formula to create the formula of the oneway.testfunction.
A simplified version of the function is:
anova_table <- function(df, dv, group){
dv_t <- deparse(substitute(dv))
group_t <- deparse(substitute(group))
anova <- oneway.test(formula = formula(paste(dv_t, "~", group_t)),
data = df,
var.equal = F)
return(anova)
}
It works fine when I use it outside a loop:
data("mpg")
mpg <- mpg %>% mutate_if(is.character, as.factor)
anova_table(mpg, displ, drv)
However, I'd like it to work also inside a loop.
When I try the following code, I get this error message:
"Error in model.frame.default(formula = formula(paste(dv_t, "~", group_t)), :
object is not a matrix"
I'm not sure what I'm doing wrong.
vars_sel <- mpg %>% select(where(is.numeric)) %>% names()
vars_sel <- dput(vars_sel)
vars_sel <- syms(vars_sel)
for(i in vars_sel){
var <- sym(i)
print(anova_table(mpg, var, drv))
}
Any help would be much appreciated!

Answer 1

Because of how your function works, the var in your loop is being taken literally, so the function is looking for a column called var in mpg which doesn't exist. You can get round this by building and evaluating a call to your function in the loop:
for(i in vars_sel){
a <- eval(as.call(list(anova_table, df = mpg, dv = i, group = quote(drv))))
print(a)
}
#>
#> One-way analysis of means (not assuming equal variances)
#>
#> data: displ and drv
#> F = 143.9, num df = 2.000, denom df = 67.605, p-value < 2.2e-16
#>
#>
#> One-way analysis of means (not assuming equal variances)
#>
#> data: year and drv
#> F = 0.59072, num df = 2.000, denom df = 67.876, p-value = 0.5567
#>
#>
#> One-way analysis of means (not assuming equal variances)
#>
#> data: cyl and drv
#> F = 129.2, num df = 2.000, denom df = 82.862, p-value < 2.2e-16
#>
#>
#> One-way analysis of means (not assuming equal variances)
#>
#> data: cty and drv
#> F = 89.54, num df = 2.000, denom df = 78.879, p-value < 2.2e-16
#>
#>
#> One-way analysis of means (not assuming equal variances)
#>
#> data: hwy and drv
#> F = 127.14, num df = 2.000, denom df = 71.032, p-value < 2.2e-16
Created on 2022-09-25 with reprex v2.0.2