the example with `pull` before, traverses the iterator's beginning twice...
what one probably wants is:
julia> function pull(itr,n::Int)
state = start(itr)
head = eltype(itr)[]
while n>0 && !done(itr,state)
val,state = next(itr,state)
push!(head,val)
n-=1
end
(head,rest(itr,state))
end
pull (generic function with 2 methods)
julia> head,tail = pull([1,2,3,4,5],3)
([1,2,3],Base.Rest{Array{Int64,1},Int64}([1,2,3,4,5],4))
julia> collect(tail)
2-element Array{Any,1}:
4
5
note the first call already pulls the first 3 elements and collects them
into an array (one can't get to the next elements without first reading the
head.
On Monday, November 9, 2015 at 10:39:48 PM UTC+2, andrew cooke wrote:
>
>
> oh that's interesting. this is from
> https://github.com/JuliaLang/Iterators.jl i guess.
>
> it doesn't support read though (which i didn't realise i needed when i
> first asked).
>
> i'll add a warning to StatefulIterators pointing people to this.
>
> thanks,
> andrew
>
> On Monday, 9 November 2015 17:07:52 UTC-3, Dan wrote:
>>
>> XXX in your questions = chain.
>> Or more clearly:
>> julia> stream = chain([1,2,3,4,5])
>> Iterators.Chain(Any[[1,2,3,4,5]])
>>
>> julia> collect(take(stream, 3))
>> 3-element Array{Any,1}:
>> 1
>> 2
>> 3
>>
>>
>> On Monday, November 9, 2015 at 7:47:51 PM UTC+2, andrew cooke wrote:
>>>
>>>
>>> hmmm. maybe i'm doing it wrong as that only gives a factor of 2 speedup.
>>>
>>> anyway, it's all i need for now, i may return to this later.
>>>
>>> thanks again,
>>> andrew
>>>
>>> On Monday, 9 November 2015 14:11:55 UTC-3, andrew cooke wrote:
>>>>
>>>>
>>>> yes, i'm about to do it for arrays (i don't care about performance
>>>> right now, but i want to implement read with type conversion and so need
>>>> the types).
>>>>
>>>> On Monday, 9 November 2015 11:20:47 UTC-3, Yichao Yu wrote:
>>>>>
>>>>> On Mon, Nov 9, 2015 at 8:04 AM, andrew cooke <and...@acooke.org>
>>>>> wrote:
>>>>> >
>>>>> > https://github.com/andrewcooke/StatefulIterators.jl
>>>>>
>>>>> FYI, one way to make this more efficient is to parametrize the
>>>>> iterator. You could easily do this for Array's. In the more general
>>>>> case, you needs type inference to get the type right for a
>>>>> non-type-stable iterator (iterator with a type unstable index...) but
>>>>> it's generally a bad idea to write code that calls type inference
>>>>> directly.
>>>>>
>>>>> >
>>>>> >
>>>>> > On Monday, 9 November 2015 06:24:14 UTC-3, andrew cooke wrote:
>>>>> >>
>>>>> >> thanks!
>>>>> >>
>>>>> >> On Sunday, 8 November 2015 22:40:53 UTC-3, Yichao Yu wrote:
>>>>> >>>
>>>>> >>> On Sun, Nov 8, 2015 at 8:11 PM, andrew cooke <and...@acooke.org>
>>>>> wrote:
>>>>> >>> > I'd like to be able to use take() and all the other iterator
>>>>> tools with
>>>>> >>> > a
>>>>> >>> > stream of data backed by an array (or string).
>>>>> >>> >
>>>>> >>> > By that I mean I'd like to be able to do something like:
>>>>> >>> >
>>>>> >>> >> stream = XXX([1,2,3,4,5])
>>>>> >>> >> collect(take(stream, 3))
>>>>> >>> > [1,2,3]
>>>>> >>> >> collect(take(stream, 2))
>>>>> >>> > [4,5]
>>>>> >>> >
>>>>> >>> > Is this possible? I can find heavyweight looking streams for
>>>>> IO, and I
>>>>> >>> > can
>>>>> >>> > find lightweight iterables without state. But I can't seem to
>>>>> find the
>>>>> >>> > particular mix described above.
>>>>> >>>
>>>>> >>> Jeff's conclusion @ JuliaCon is that it seems impossible to
>>>>> implement
>>>>> >>> this (stateful iterator) currently in a generic and performant way
>>>>> so
>>>>> >>> I doubt you will find it in a generic iterator library (that works
>>>>> not
>>>>> >>> only on arrays). A version that works only on Arrays should be
>>>>> simple
>>>>> >>> enough to implement and doesn't sound useful enough to be in an
>>>>> >>> exported API so I guess you probably should just implement your
>>>>> own.
>>>>> >>>
>>>>> >>> Ref
>>>>> >>>
>>>>> https://groups.google.com/forum/?fromgroups=#!searchin/julia-users/iterator/julia-users/t4ZieI2_iwI/3NTw1k406qkJ
>>>>>
>>>>> >>>
>>>>> >>> >
>>>>> >>> > (I think I can see how to write it myself; I'm asking if it
>>>>> already
>>>>> >>> > exists -
>>>>> >>> > seems like it should, but I can't find the right words to search
>>>>> for).
>>>>> >>> >
>>>>> >>> > Thanks,
>>>>> >>> > Andrew
>>>>> >>> >
>>>>>
>>>>
