Functional programming

Built-in Higher Order Functions

R has a set of built in higher order functions: Map, Reduce, Filter, Find, Position, Negate.

Map applies a given function to a list of values:

words <- list("this", "is", "an", "example")
Map(toupper, words)

Reduce successively applies a binary function to a list of values in a recursive fashion.

Reduce(`*`, 1:10)

Filter given a predicate function and a list of values returns a filtered list containing only values for whom predicate function is TRUE.

Filter(is.character, list(1,"a",2,"b",3,"c"))

Find given a predicate function and a list of values returns the first value for which the predicate function is TRUE.

Find(is.character, list(1,"a",2,"b",3,"c"))

Position given a predicate function and a list of values returns the position of the first value in the list for which the predicate function is TRUE.

Position(is.character, list(1,"a",2,"b",3,"c"))

Negate inverts a predicate function making it return FALSE for values where it returned TRUE and vice versa.

is.noncharacter <- Negate(is.character)
is.noncharacter("a")
is.noncharacter(mean)