# fold: Efficient Fold, Reduce, Accumulate, Combine of a Vector In future.apply: Apply Function to Elements in Parallel using Futures

## Description

Efficient Fold, Reduce, Accumulate, Combine of a Vector

## 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"`. `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[], x[]), x[])` equals `f(x[], f(x[]), x[])`.

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

## Value

A vector.

future.apply documentation built on Aug. 10, 2021, 5:06 p.m.