funprog: Higher Order Functions

In cmann3/eList: List Comprehension and Tools

Description

Common functions used in functional programming. These are similar to their respective counterparts in Base R: Map, Reduce, Filter, etc. However, they take any value that can be converted to a function via lambda and the function comes after the argument in the argument list for convenience while piping.

Usage

map(
  x,
  f,
  ...,
  simplify = FALSE,
  USE.NAMES = FALSE,
  FUN.VALUE = NULL,
  clust = NULL
)

mapn(
  f,
  ...,
  simplify = FALSE,
  USE.NAMES = FALSE,
  FUN.VALUE = NULL,
  clust = NULL
)

ffind(x, f, ...)

filter(x, f, ...)

reduce(x, f, init = NULL, right = FALSE)

accumulate(x, f, init, right = FALSE)

compose(...)

Arguments

x	vector
f	function to be applied to x
...	additional arguments supplied to f, or a list of functions for compose (applied in the order provided)
simplify	logical; should the results be simplified to an array?
USE.NAMES	logical; should x be used as names for the result?
FUN.VALUE	template vector for the return type
clust	cluster to use for parallel computations. See comprehension for more details. FUN.VALUE is ignored if a cluster is supplied.
init	object used to initialize reduce, if an object other then the first value is desired
right	logical; should the reduction start from left (default) or right?

Details

map is slightly different from Map in Base R other than the argument order. First, iter is applied to the vector x so that users can define behavior for custom classes. Second, lambda is applied to f. map only works for a single vector. Use mapn to use multiple vectors as the function argument. The map functions are wrappers around sapply or link[base]{vapply} (if FUN.VALUE is provided).

The other functions behave similar to what one would expect, with the exception of accumulate. accumulate does not produce all intermediate results; it only provides the final cumulative vector.

compose takes multiple functions and produces a single "composed" function. When the composed function is called, each function in the list is applied sequentially to the arguments. The functions can be retrieved from the composed function's attributes.

Value

determined by the return value of the function f.

Functions

• map: Apply function f using elements in vector x at each index.

• mapn: Apply function f using the element in all elements in vectors ... at each index as arguments.

• ffind: Find the position of elements in vector x that satisfy predicate function f.

• filter: Extract elements in vector x that satisfy predicate function f.

• reduce: Combine elements in a vector x using binary function f.

• accumulate: Combine elements in a vector x using binary function f, accumulating the results.

• compose: Combine functions into a single function.

Examples

x <- list(1:3, 4:6, 7:9)
map(x, ~Reduce(`-`, .i))
map(x, sqrt)

filter(x[[1]], ~.i < 3)

reduce(x[[3]], `*`, init=1)

f <- compose(sqrt, log, `*`(2))
f(10)

cmann3/eList documentation built on Jan. 25, 2021, 6:17 a.m.