Functional data structure

Functional data structures are special forms of data structure, which are implemented primarily in functional programming languages. R supports functional programming by providing tools for creation and manipulation of functions. For example, R support assigning functions to variables and passing them as an argument within a function. The R support generating the function dynamically and returning them as a result of the function is also known as a closure function. For example, the function which takes a function as an argument is shown as follows:

arg_function <- function(g) g(seq(1, 100, by=1))

The function arg_function can take functions as an argument, such as mean or sd as shown in the following code snippet:

> arg_function(mean)
[1] 50.5
> arg_function(sd)
[1] 29.01149

The functional data structure is also known as persistent data structure as they are immutable in the sense that any operation performed on function data structure...