Extract values from list of named lists in R - r

Question

Based on the names of sublists with xyz values of a list, I would like to extract a sample of the xyz values from a sublist. Note: the lists do not start at 1.
Example data
set.seed(123)
data <- list('4' = list(x = rnorm(5), y = rnorm(5), z = rnorm(5)),
'5' = list(x = rnorm(5), y = rnorm(5), z = rnorm(5)),
'6' = list(x = rnorm(5), y = rnorm(5), z = rnorm(5)),
'7' = list(x = rnorm(5), y = rnorm(5), z = rnorm(5)),
'8' = list(x = rnorm(5), y = rnorm(5), z = rnorm(5)))
Function to extract random values (derived from here)
I have the following function to sample random xyz values from the list:
get_elements <- function(data, i) {
#select the main list
tmp <- data[[i]]
#Check the length of each sublist, select minimum value
#and sample 1 number from 1 to that number
rand_int <- sample(min(lengths(tmp)), 1)
#select that element from each sub-list
sapply(tmp, `[[`, rand_int)
}
Example of function
# Show list number 8
data[['8']]
#> $x
#> [1] 0.3796395 -0.5023235 -0.3332074 -1.0185754 -1.0717912
#> $y
#> [1] 0.30352864 0.44820978 0.05300423 0.92226747 2.05008469
#> $z
#> [1] -0.4910312 -2.3091689 1.0057385 -0.7092008 -0.6880086
# Extract random combination from list 8
get_elements(data, '8')
#> x y z
#> -0.33320738 0.05300423 1.00573852
Rewrite function
Using the same function as above, I replaced i with 'i':
get_elements <- function(data, i) {
tmp <- data[['i']] # <-- changed i to 'i'
rand_int <- sample(min(lengths(tmp)), 1)
sapply(tmp, `[[`, rand_int)
}
Error & Question
get_elements(data, 8)
Warning in min(lengths(tmp)): no non-missing arguments to min;
returning Inf list()
Suddenly the function breaks, and I do not understand why? What is the reason for this error?

Answer 1

Try this:
get_elements <- function(data, i)
{
tmp <- data[[paste(i)]]
rand_int <- sample(min(lengths(tmp)), 1)
sapply(tmp, `[[`, rand_int)
}
The reason your initial code failed is because "i" is understood as "character i", not as "convert variable i into character". See:
i = 1
print("i") # i
print(i) # 1