fold: Efficient fold / reduce / accumulate / combine of a vector

Description Usage Arguments Details Value

View source: R/fold.R

Description

This function comes from the future.apply package.

Usage

1
fold(x, f, left = TRUE, unname = TRUE, threshold = 1000L)

Arguments

x

A vector.

f

A binary function, i.e. a function take takes two arguments.

left

If TRUE, vector is combined from the left (the first element), otherwise the right (the last element).

unname

If TRUE, function f is called as f(unname(y), x[[ii]]), otherwise as f(y, x[[ii]]), which may introduce name "y".

[[ii]: R:[ii [[ii]: R:[ii

threshold

An integer (>= 2) specifying the length where the recursive divide'and'conquer call will stop and incremental building of the partial value is performed. Using threshold = +Inf will disable recursive folding.

Details

In order for recursive folding to give the same results as non-recursive folding, binary function f must be associative with itself, i.e. f(f(x[[1]], x[[2]]), x[[3]]) equals f(x[[1]], f(x[[2]]), x[[3]]).

This function is a more efficient (memory and speed) of [base::Reduce(f, x, right = !left, accumulate = FALSE)][base::Reduce], especially when x is long.

[[1]: R:[1 [[2]: R:[2 [[3]: R:[3 [[1]: R:[1 [[2]: R:[2 [[3]: R:[3 [base::Reduce]: R:base::Reduce

Value

A vector.


furrr documentation built on May 2, 2019, 1:04 p.m.