Add level to R Data frame - r

Question

Let's say we have a data frame/table organized like this
x$user1, x$user2, etc..
x$usern is a data table with attributes like $age, $department, $sale, $price, etc.
I would like to "push" and regroup the data frame in x$usern to one lower level, so that I can add other data tables below x$usern
Perhaps it's better with illustration : the current structure is
x
$user1 $user2
$price,$age, etc. $price, $age, etc.
Target structure is
x
$user1 $user2
$data $stat $data $stat
$price,$age, etc. $min, $max, etc. $price,$age, etc. $min, $max, etc.
What would be the best way to achieve this. I am thinking of lapply and/or loop through all user, but perhaps there is a more elegant way to do this ?
Thank you.

Answer 1

This seems like a good place for lapply (or one of its kin). Some mock data:
x <- list(
user1 = data.frame(price = 11, age = 12),
user2 = data.frame(price = 21, age = 22)
)
str(x)
# List of 2
# $ user1:'data.frame': 1 obs. of 2 variables:
# ..$ price: num 11
# ..$ age : num 12
# $ user2:'data.frame': 1 obs. of 2 variables:
# ..$ price: num 21
# ..$ age : num 22
The transformation:
newx <- lapply(x, function(l) {
st <- data.frame(min = 0.9*min(l$price), max = 1.1*max(l$age))
list(data = l, stat = st)
})
str(newx)
# List of 2
# $ user1:List of 2
# ..$ data:'data.frame': 1 obs. of 2 variables:
# .. ..$ price: num 11
# .. ..$ age : num 12
# ..$ stat:'data.frame': 1 obs. of 2 variables:
# .. ..$ min: num 9.9
# .. ..$ max: num 13.2
# $ user2:List of 2
# ..$ data:'data.frame': 1 obs. of 2 variables:
# .. ..$ price: num 21
# .. ..$ age : num 22
# ..$ stat:'data.frame': 1 obs. of 2 variables:
# .. ..$ min: num 18.9
# .. ..$ max: num 24.2
(Obviously, my definition of st would have to be tailored to your needs. Additionally, it does not strictly need to be defined within the lapply, but it makes sense to do it there if you already know its definition based on x$user1$....)