its possible to nest comprehensions:
[ [x[y] for x in mytuple] for y=1:2 ]
this expression can be splatted like you suggested.
On Thursday, July 17, 2014 3:53:42 PM UTC+3, Tomas Lycken wrote:
>
> That's neat! Thanks!
>
> However, it only got me *almost* there - my next step was to use these
> arrays as function arguments, so I want to use `...` splatting. However,
> `foo([x[y] for x in mytuples,y=1:2]...)` will splat the entire matrix
> element-wise, instead of row-wise.
>
> Is there a way to get it into two `Array{Float64,1}` objects, rather than
> an `Array{Float64,2}`, and still only use it in one expression?
>
> (Yes, I realize I'm starting to make things more complicated than they
> need to be, but this is an opportunity to learn new ways of doing things -
> not just an attempt to get things done :P)
>
> // T
>
> On Thursday, July 17, 2014 2:05:38 PM UTC+2, David Gonzales wrote:
>>
>> it is possible to use two indices in a comprehension:
>> mat = [x[y] for x in mytuples,y=1:2]
>> now mat[:,1] is your first vector, and mat[:,2] is the second.
>>
>> On Thursday, July 17, 2014 12:37:20 PM UTC+3, Tomas Lycken wrote:
>>>
>>> I have an array of 2-tuples of floats, created as
>>>
>>> julia> mytuples = (Float64,Float64)[(v.x, v.y for v in vs] # slightly more
>>> complicated in actual code
>>> 136-element Array{(Float64,Float64),1}:
>>> (4.0926,-2.55505)
>>> (4.170826,-2.586752)
>>>
>>> ...
>>>
>>> Now, I’d like to split this into two arrays of floats. I was under the
>>> impression that zip could do this for me - according to the docs, zip
>>> is its own inverse
>>> <http://docs.julialang.org/en/latest/stdlib/base/#Base.zip>, and the
>>> array of tuples does look like something I could get from zipping two
>>> arrays. So I tried something similar to the example there:
>>>
>>> julia> julia> [zip(mytuples...)...]
>>> 2-element Array{(Float64,Float64,Float64, ... and so on, 136 times...),1}:
>>>
>>> so I guess that only works on actual Zip objects, and not on arrays
>>> (that could have been) generated by the zip function inside []. (Also,
>>> since this uses splatting with ... on large lists, it might not be a
>>> good idea in the first place…?
>>> <https://github.com/JuliaLang/julia/issues/6098#issuecomment-37203821>)
>>>
>>> What’s the best way to accomplish what I want, i.e. transforming the
>>> mytuple variable above into two Vector{Float64}s (possibly inside a
>>> tuple or array or something)?
>>>
>>> // T
>>>
>>>
>>
