Re: [julia-users] Re: Periodic or cyclic arrays possible?

[Erik Schnetter]

The expression `(i-1) % length + 1` is not correct for negative `i`.
You have to use `mod` instead of `%`.

Julia has a function `mod1(x,y)` that is essentially defined as
`mod(x-1, y) +1`, so that's what you probably want to use.

-erik

On Sat, Feb 6, 2016 at 8:40 PM, Cedric St-Jean  wrote:
> You can define our own datatype to do this. It's one of the most fundamental
> tasks in Julia!
>
> immutable CircularArray{T}
> arr::Vector{T}
> end
>
> Base.getindex(ca::CircularArray, i) = ca.arr[(i-1) % length(ca.arr) + 1]
> Base.setindex(...) = ...
> ...
>
> a = CircularArray([1,2,3])
> a[14] # yields 2
>
> Cédric
>
>
> On Saturday, February 6, 2016 at 7:08:03 PM UTC-5, Ferran Mazzanti wrote:
>>
>> Hi folks,
>>
>> I was wondering if it is possible to use in a simple way cyclic arrays in
>> Julia? What I'm after is sometbing that understands that the next element in
>> a[] after end is a[1], so a[end+1]=a[1], a[end+2]=a[2] etc... I know I can
>> index the array with the remainder operator % to achieve this same result,
>> but I wonder if one can declare the array directly in one way or another to
>> achieve this directly.
>>
>> Thanks in advance,
>>
>> Ferran.



-- 
Erik Schnetter 
http://www.perimeterinstitute.ca/personal/eschnetter/

Re: [julia-users] Re: Periodic or cyclic arrays possible?

[Matt Bauman]

I highly recommend reading the Interfaces chapter[1] for a walk-through on 
creating your own array type.  Another great trick that you can use is 
`A[mod1(x, end)]`.

1. http://docs.julialang.org/en/release-0.4/manual/interfaces/

On Sunday, February 7, 2016 at 10:52:45 AM UTC-5, Erik Schnetter wrote:
>
> The expression `(i-1) % length + 1` is not correct for negative `i`. 
> You have to use `mod` instead of `%`. 
>
> Julia has a function `mod1(x,y)` that is essentially defined as 
> `mod(x-1, y) +1`, so that's what you probably want to use. 
>
> -erik 
>
> On Sat, Feb 6, 2016 at 8:40 PM, Cedric St-Jean  > wrote: 
> > You can define our own datatype to do this. It's one of the most 
> fundamental 
> > tasks in Julia! 
> > 
> > immutable CircularArray{T} 
> > arr::Vector{T} 
> > end 
> > 
> > Base.getindex(ca::CircularArray, i) = ca.arr[(i-1) % length(ca.arr) + 1] 
> > Base.setindex(...) = ... 
> > ... 
> > 
> > a = CircularArray([1,2,3]) 
> > a[14] # yields 2 
> > 
> > Cédric 
> > 
> > 
> > On Saturday, February 6, 2016 at 7:08:03 PM UTC-5, Ferran Mazzanti 
> wrote: 
> >> 
> >> Hi folks, 
> >> 
> >> I was wondering if it is possible to use in a simple way cyclic arrays 
> in 
> >> Julia? What I'm after is sometbing that understands that the next 
> element in 
> >> a[] after end is a[1], so a[end+1]=a[1], a[end+2]=a[2] etc... I know I 
> can 
> >> index the array with the remainder operator % to achieve this same 
> result, 
> >> but I wonder if one can declare the array directly in one way or 
> another to 
> >> achieve this directly. 
> >> 
> >> Thanks in advance, 
> >> 
> >> Ferran. 
>
>
>
> -- 
> Erik Schnetter  
> http://www.perimeterinstitute.ca/personal/eschnetter/ 
>

[julia-users] Re: Periodic or cyclic arrays possible?

[Cedric St-Jean]

You can define our own datatype to do this. It's one of the most 
fundamental tasks in Julia!

immutable CircularArray{T}
arr::Vector{T}
end

Base.getindex(ca::CircularArray, i) = ca.arr[(i-1) % length(ca.arr) + 1]
Base.setindex(...) = ...
...

a = CircularArray([1,2,3])
a[14] # yields 2

Cédric

On Saturday, February 6, 2016 at 7:08:03 PM UTC-5, Ferran Mazzanti wrote:
>
> Hi folks,
>
> I was wondering if it is possible to use in a simple way cyclic arrays in 
> Julia? What I'm after is sometbing that understands that the next element 
> in a[] after end is a[1], so a[end+1]=a[1], a[end+2]=a[2] etc... I know I 
> can index the array with the remainder operator % to achieve this same 
> result, but I wonder if one can declare the array directly in one way or 
> another to achieve this directly.
>
> Thanks in advance,
>
> Ferran.
>
>