Functional tools for R

This module provides a basic toolbox for working with functions in R.

box::use(klmr/fun)

Creating functions

Use closure to create a function:

twice = fun$closure(alist(x =), quote(x * 2), globalenv())
twice

## function (x) 
## x * 2

twice(10)

## [1] 20

Function composition

Use compose to compose functions:

four_times = fun$compose(twice, twice)
four_times(2)

## [1] 8

Alternatively, use one of the function composition operators:

box::use(klmr/fun[...]) # Attach module to use operators.

# Traditional order of arguments, same as `compose`:
sd1 = sqrt %.% var
sd1(CO2$uptake)

## [1] 10.81441

# Alternative order:
sd2 = var %|>% sqrt
sd2(CO2$uptake)

## [1] 10.81441

Function chaining

As made popular by ‘magrittr’ and ‘dplyr’:

CO2$uptake %>% var() %>% sqrt()

## [1] 10.81441

Note the similarity in usage between %>% and %|>%.

Partial function application

Partial function application via partial creates a new function with fewer arguments.

box::use(klmr/fun[p = partial])

minus1 = p(`-`, 1)
sapply(1 : 5, minus1)

## [1] 0 1 2 3 4

These higher-order functions become powerful when combined, and easily construct complex anonymous functions.

strrev =
    p(strsplit, '') %|>%
    p(lapply, rev) %|>%
    p(lapply, p(paste, collapse = '')) %|>%
    unlist
strrev(c('foo', 'bar'))

## [1] "oof" "rab"

A concise lambda syntax

box::use(klmr/fun/lambda[...])

sapply(1 : 4, x -> 2 * x)

## [1] 2 4 6 8

mapply(x ~ y -> x + y, 1 : 4, 5 : 8)

## [1]  6  8 10 12

• var -> expr is equivalent to function (var) expr.

• x ~ y -> expr is equivalent to function (x, y) expr. An arbitrary number of arguments is supported.

Note: Importing this submodule changes the semantics of <- (since <- and -> refer to the same operator in R). Consequently, this module can only be used in code that uses = for assignment.