How to extract the first item in a list(even if the list is empty)

Question

In R, I want to extract the first item from a nested list of lists; however sometimes the list might be empty.

e.g.:

myList <- list(
            list(ID = 1, Sales = 1000, Product = "Car"),
            list(ID = 2, Sales = 2000, Product = "Boat"),
            list(ID = 3, Sales = 1500, Product = "Bike")
)
myList2 <- list()

So when I make the following call:

myList[[1]]
myList2[[1]]

The first call returns a valid sub-list (ID=1, Sales=1000, Product = "Car") but the second call returns an error -

Error in myList2[[1]] : subscript out of bounds

Is there a simple call I can make that says "return item 1 when the list is populated, otherwise return NULL and do not throw an error"?

Answer 1

We can create a function to return NULL if the length is 0 or else to return the subset of the list

f1 <- function(lst, ind){
   if(length(lst) >=1) lst[[ind]] else NULL
}

f1(myList2, 1)
#NULL

f1(myList, 1)
#$ID
#[1] 1

#$Sales
#[1] 1000

#$Product
#[1] "Car"

Answer 2

You can use the first function of dplyr package:

first(myList, default = NULL)
first(myList2, default = NULL)

More info on that function here: https://dplyr.tidyverse.org/reference/nth.html