R: Efficient Fold, Reduce, Accumulate, Combine of a Vector

fold {future.apply} | R Documentation

## Efficient Fold, Reduce, Accumulate, Combine of a Vector

### Description

Efficient Fold, Reduce, Accumulate, Combine of a Vector

### Usage

    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[[1]], x[[2]]), x[[3]])` equals `f(x[[1]], f(x[[2]]), x[[3]])`.

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.

[Package future.apply version 1.0.1 Index]