R - Subsetting subsets of variable names in loops - r

Question

Q: How do I subset a subset of a changing variable inside a function or loop?
Assume I have the following code for determining regression stats for multiple data sets :
dat1 <- data.frame(col1=1:5,col2=6:10)
dat2 <- data.frame(col1=11:15,col2=16:20)
func <- function(data,col.no){
get(data)[,col.no]
}
for(i in c('dat1','dat2')) {
mod.name <- paste0('fit.',i)
assign(mod.name,lm(get(i)[,1]~get(i)[,2]),envir = .GlobalEnv)
}
mod.pvals <- NULL
p.func <- function(attr.name) {
for(i in c('dat1','dat2')) {
mod.name <- paste0('fit.',i)
p.val <- summary(get(mod.name))[attr.name]
mod.pvals <- c(mod.pvals,p.val)
}
mod.pvals
}
r.vals <- p.func('r.squared')
adj.r.vals <- p.func('adj.r.squared')
coef.vals <- p.func('coefficients')
This works just fine with 'r.squared','adj.r.squared',etc.
But I want to access the p-value of the model in the same function.
Outside of a function I'd choose:
summary(fit)$coefficients[2,4]
But how do I do this inside of the function??
I unsuccessfully tried:
summary(get(mod.name))['coefficients'][2,4]
Error in summary(get(mod.name))["coefficients"][[2, 4]] :
incorrect number of subscripts
So then I thought about just changing my code for p.val in the function above:
p.val <- paste0('summary(',mod.name ,')$',attr.name)
get(p.val)
But when I run the code I get the following error:
p.vals <- p.func('coefficients[2,4]')
Error in get(p.val) :
object 'summary(fit.dat1)$coefficients[2,4]' not found
I guess get() doesn't work like this. Is there a function that I can replace get() with?
Other thoughts on how I could make this work??

Answer 1

One solution is to use eval() and parse():
p.val <- eval(parse(text=paste0("summary(",mod.name,")[",paste0(attr.name),"]")))
So the function would be:
mod.pvals <- NULL
p.func <- function(attr.name) {
for(i in c('dat1','dat2')) {
mod.name <- paste0('fit.',i)
p.val <- eval(parse(text=paste0("summary(",mod.name,")[",attr.name,"]")))
mod.pvals <- c(mod.pvals,p.val)
}
mod.pvals
}
r.vals <- p.func(attr.name = '\'r.squared\'')
p.vals <- p.func(attr.name = '[\'coefficients\']][2,4')