Nest data inside loop - r

Question

I'm currently having an issue where I'm trying to nest simulated data for an efficient frontier inside a tibble containing all 250 simulations. The tibble will have 1 column named "sim" which indicates the number of the simulation, i.e. the rows in this column runs from 1:250. The other column should contain the nested simulation data which is a 3x123 tibble for each simulation. (Really hope this makes sense).
I've tried to replicate the problem such that you don't need all of the previous code and data to see the issue. Problem is that the nested data is saved as a list:
library(tidyverse)
counter = 0
table <- tibble(sim = 1:250, obs = NA)
for(i in (1:250)){
counter = counter + 1
tibble <- tibble(a = NA, b = 1:113, c = 2, d = 3)
tibble$a <- counter
nested_tibble <- tibble %>% nest(data = -a) %>% select(-a)
table$obs[i] <- nested_tibble
}
In this simplified reproducible example the values in the tibble are identical. Whereas in the assignment I'm working on, the tibble contains values for the efficient frontier. Variable 'a' in the tibble corresponds to simulation number and this is the variable i use to nest the efficient frontier. Afterwards I wish to remove this variable a, and insert the nested tible in the corresponding 'obs' field currently being NA.
I really hope this makes sense. I'm still very new with R and coding. If you need any additional documentation please let me know.

Answer 1

Your nested_tibble is a list containing a tibble. To access the tibble inside the list, you can use double bracket notation: nested_tibble[[1]]. So to get the result you want you can change your loop as follows:
counter = 0
table <- tibble(sim = 1:250, obs = NA)
for(i in (1:250)){
counter = counter + 1
tibble <- tibble(a = NA, b = 1:113, c = 2, d = 3)
tibble$a <- counter
nested_tibble <- tibble %>% nest(data = -a) %>% select(-a)
table$obs[i] <- nested_tibble[[1]]
}