recursiveiter {combiter}

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], "")