Package 'combiter'

First Value of Iterator

Description

getFirst is a generic function that returns the first value of iterators

Usage

getFirst(obj, ...)

Arguments

obj	an R object
...	additional arguments

Value

iterator value, format dependes on the objects

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Last Value of Iterator

Description

getFirst is a generic function that returns the last value of iterators

Usage

getLast(obj, ...)

Arguments

obj	an R object
...	additional arguments

Value

iterator value, format dependes on the objects

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Does This Iterator Have A Previous Element

Description

hasPrev is a generic function that indicates if the iterator has another element backward.

Usage

hasPrev(obj, ...)

Arguments

obj	an R object
...	additional arguments

Value

Logical value indicating whether the iterator has a previous element.

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Cartesian Product Iterator

Description

Create an iterator going through Cartesian product of several items.

Usage

icartes(nvec)

icartesv(...)

Arguments

nvec	integer vector of number of items
...	set of iterables (subsettable by [)

Details

• icartes iterates through all combinations of integers

• icartesv iterates through all combinations of general values

Value

iterator object

Examples

x <- icartes(c(3, 2, 4))
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}

x <- icartesv(Month=c("Jan", "Feb", "Mar"),
              Loc=c("NY", "LA"),
              By=c("car", "plane", "bus"))
as.list(x)

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Combination Iterator

Description

Create an iterator for all combinations k integers out of 1 through n.

Usage

icomb(n, k)

icombv(values, k)

Arguments

n	positive integer
k	positive integer no greater than n
values	iterable (subsettable by [)

Details

• icomb iterates through integer vectors

• icombv iterates through general values

Value

iterator object

Examples

x <- icomb(5, 3)
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}

as.list(icombv(c("A", "G", "C"), 2))

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Permutation Iterator

Description

Create an iterator for all permutations of size k of integers 1 to n.

Usage

iperm(n, k = n)

ipermv(values, k = length(values))

Arguments

n	positive integer
k	positive integer
values	iterable (subsettable by [)

Details

• iperm iterates through integer vectors

• ipermv iterates through general values

Value

iterator object

Examples

x <- iperm(3)
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}


as.list(ipermv(c("R", "G", "B")))

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Subset Iterator

Description

Create an iterator for all subsets of integers 1 through n.

Usage

isubset(n)

isubsetv(values)

Arguments

n	positive integer
values	iterable (subsettable by [)

Details

• isubset iterates through integer vectors

• isubsetv iterates through general values

Value

iterator object

Examples

x <- isubset(3)
ct <- 0
while (hasNext(x))
{
  ct <- ct + 1
  i <- nextElem(x)
  cat(sprintf("%3d : %s\n", ct, paste0(i, collapse = " ")))
}

as.list(isubsetv(letters[1:4]))

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Get Previous Element of Iterator

Description

prevElem is a generic funcion to move an iterator object one step backward.

Usage

prevElem(obj, ...)

Arguments

obj	an R object
...	additional arguments

Value

iterator value

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Factory of Iterators defined by Recursive Transition Functions

Description

This is a constructor for custom iterator objects. It requires four functions, "next", "prev", "first", and "last", and additional parameters.

The state of the constructor is characterized by the variable i. The "next" and "prev" function must take i and the parameters and return the next and previous state variables respectively. The behavior where there is no more state left is arbitrary.

The "first" and "last" functions must take the additional parameters and return the initial and last state variables respectively.

The created object is an iterator of class recursiveiter, which inherits abstractiter and iter. It can be used with foreach and accepts as.list conversion.

Usage

recursiveiter(nextFunc, prevFunc, firstFunc, lastFunc, ...)

Arguments

nextFunc, prevFunc	Functions that take the iterator state and the parameters ... and returns the next or previous state
firstFunc, lastFunc	Functions that take the parameters ... and returns the first or last state of the iteration
...	additional parameters of the iterator

Value

iterator object

Examples

fibiter <- recursiveiter(
  nextFunc = function(i) if (length(i)==1 && i==0) 1 else
                         if (length(i)==1 && i==1) c(1,1) else
                         c(sum(i), i[1]),
  prevFunc = NULL, firstFunc = function() 0, lastFunc = function() Inf)
for (k in 1:20) cat(nextElem(fibiter)[1], "")

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