What's the name of the first argument of `[`?

Question

letter[2] is equivalent to '['(letters,i=2) , second argument is i.

What is the name of the first argument so the 2 following expressions would be equivalent ?

lapply(1:3,function(x){letters[x]})
lapply(1:3,`[`,param1 = letters) # param1 to be replaced with solution

Answer 1

For you to be able to define a function similar to the one above, you will have to pass two arguments to your function. The function [ does take various inputs. We can use Map instead of lapply to give it both the data where to extract from and the Indices to indicate the part of the data to be extracted:

  Map("[",list(letters),1:3)
 [[1]]
 [1] "a"

 [[2]]
 [1] "b"

 [[3]]
 [1] "c"

This is similar to what you have above. Hope this helps

Answer 2

You have to be could be more specific than "[", for instance:

lapply(1:3, `[.numeric_version`, x = letters)

# [[1]]
# [1] "a"
# 
# [[2]]
# [1] "b"
# 
# [[3]]
# [1] "c"

(Not sure [.numeric_version is the most appropriate, though... I'm digging a bit more)