Conditional selection of elements of a list in Base R - r

Question

I'm trying to find the unique elements in the variables listed as x.
The only constraint is that I want to first find the variable (here either a, b, or c) in the list whose max element is smallest, and keep that variable untouched at the top of the output?
I have tried something but can't implement the constraint above:
P.S. My goal is to achieve a function/looping structure to handle larger lists.
x = list(a = 1:5, b = 3:7, c = 6:9) ## a list of 3 variables; variable `a` has the smallest
## max among all variables in the list, so keep `a`
## untouched at the top of the output.
x[-1] <- Map(setdiff, x[-1], x[-length(x)]) ## Now, take the values of `b` not shared
## with `a`, AND values of `c` not shared
## with `b`.
x
# Output: # This output is OK now, but if we change order of `a`, `b`,
# and `c` in the initial list the output will change.
# This is why the constraint above is necessary?
$a
[1] 1 2 3 4 5
$b
[1] 6 7
$c
[1] 8 9

Answer 1

#Find which element in the list has smallest max.
smallest_max <- which.min(sapply(x, max))
#Rearrange the list by keeping the smallest max in first place
#followed by remaining ones
new_x <- c(x[smallest_max], x[-smallest_max])
#Apply the Map function
new_x[-1] <- Map(setdiff, new_x[-1], new_x[-length(new_x)])
new_x
#$a
#[1] 1 2 3 4 5
#$b
#[1] 6 7
#$c
#[1] 8 9
We can wrap this up in a function and then use it
keep_smallest_max <- function(x) {
smallest_max <- which.min(sapply(x, max))
new_x <- c(x[smallest_max], x[-smallest_max])
new_x[-1] <- Map(setdiff, new_x[-1], new_x[-length(new_x)])
new_x
}
keep_smallest_max(x)
#$a
#[1] 1 2 3 4 5
#$b
#[1] 6 7
#$c
#[1] 8 9