How to get the nth element of each item of a list, which is itself a vector of unknown length

Question

If we have a list, and each item can have different length. For example:

l <- list(c(1, 2), c(3, 4,5), c(5), c(6,7))

(In order to be cl

Answer 1

# the source list 
source_list <- list(c(1, 2), c(3, 4,5), c(5), c(6,7))

# the index of the elements you want 
k <- 1

# the results character vector 
x <- c()

for (item in source_list) {
     x <- append(x, item[k])
   }

print(x)
[1] 1 3 5 6