iterors (version 1.0)

reduce: Compute the sum, product, or general reduction of an iterator.

Description

reduce(obj, fun) applies a 2-argument function fun between successive elements of obj. For example if fun is +, reduce(it, +, init=0) computes 0 + nextElem(it) + nextElem(it) + nextElem(it) + ... until the iterator finishes, and returns the final value.

i_accum(obj) returns the iterator containing each intermediate result. The default settings produce a cumulative sum.

sum.iteror(it) is equivalent to reduce(it, `+`)

prod.iteror(it) is equivalent to reduce(it, `*`).

Usage

reduce(obj, fun = `+`, init = 0, ...)
# S3 method for iteror
reduce(obj, fun = `+`, init = 0, ...)
i_accum(obj, fun = `+`, init = 0, ...)
# S3 method for iteror
sum(..., na.rm = FALSE)
# S3 method for iteror
prod(..., na.rm = FALSE)

Value

The result of accumulation.

Arguments

obj

an iterable object

fun

A function of as least two arguments.

init

A starting value.

...

Extra parameters will be passed to each call to fun.

na.rm

Whether to drop NA values when computing sum or prod.

Author

Peter Meilstrup

Examples

it <- icount(5)
total <- reduce(it, `+`) # 15

it <- icount(5)
reduce(it, paste0, "") # "12345"

it <- icount(5)
reduce(it, `*`, init=1) # 120

# triangular numbers: 1, 1+2, 1+2+3, ...
take(i_accum(icount()), 10, 'numeric')