How to implement an iterator in julia?

by jeanie_reilly , in category: Other , a year ago

How to implement an iterator in julia?

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2 answers

by filomena_oreilly , a year ago

@jeanie_reilly 

In Julia, you can implement an iterator by defining a type that implements the Iterator interface. The Iterator interface requires the implementation of two methods: next and done.


Here's an example implementation of an iterator that produces the Fibonacci sequence:

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struct FibonacciIterator
    state::Tuple{Int, Int}
end

Base.iterate(itr::FibonacciIterator, state=itr.state) = 
    state[1], (state[2], state[1] + state[2])

Base.iterate(itr::FibonacciIterator, state=nothing) = 
    state, state

function Base.length(itr::FibonacciIterator)
    error("length not defined for infinite iterator")
end

Base.eltype(::Type{<:FibonacciIterator}) = Int


In this implementation, FibonacciIterator is a struct that stores the current state of the iterator. The next method is defined by the iterate function. This function takes an iterator and a state and returns a tuple containing the next value and the new state of the iterator. In the first iterate method, we return the next Fibonacci number and the new state, which is the previous two Fibonacci numbers. In the second iterate method, we return the state itself, indicating that we've reached the end of the iterator. The length function is also defined to throw an error, since the Fibonacci sequence is infinite and doesn't have a defined length. Finally, the eltype function is defined to return Int, since the Fibonacci sequence is a sequence of integers.


With this implementation, we can create a Fibonacci iterator and iterate over it like this:

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fib = FibonacciIterator((0, 1))
for i in take(fib, 10)
    println(i)
end


This will print the first 10 numbers of the Fibonacci sequence. The take function is used to limit the iterator to 10 elements, since the Fibonacci sequence is infinite.

by austyn.beer , a month ago

@jeanie_reilly 

It is important to mention that the Base keyword is used to define methods for the iterator interface in Julia. The next method is called iterate in Julia and it returns two values: the next element and the new state of the iterator. The first iterate method in the example above is used when the iterator is not done yet, and the second method is used when the iterator is done. The length method is optional and can be defined if applicable, and the eltype method is used to specify the type of the elements returned by the iterator.