Accessing array inside composite type in Julia

Question

I have the following two structs. When I initialize the struct with a constructor, an array is created, but it is not what I expected.

using Distributions

mutable struct XYZ
    x::Float64
    y::Float64
    z::Float64
end

mutable struct Coords
    r::Vector{XYZ}
end

""" Make a structure called test that contains a vector of type XYZ 
I want to have 10 XYZ structs in the "r" Vector """

Coords() = ( rand(Uniform(0,1.0),10,3) )
test = Coords()

I want to access test by going test.r.x[i], however Julia complains that type Tuple has no field r. What it does create is a 2 dimensional array of size 10x3 and I can call elements via test[i,j] but this is far from what I want. I want to have other arrays/variables in the composite with callable names...

I tried initializing this way as well

XYZ() = (rand(),rand(),rand())
Coords() = ([ XYZ() for i in 1:10 ])
test = Coords()

I still get the same warning. It seems like I have created a tuple rather than a composite type. How do I create a composite type that has arrays/vectors inside of other structs?

I am using Julia version 1.0.2

Oh, and (expr) does not create a 1-tuple -- that's equivalent to just expr. To actually create a 1-tuple (which you don't actually need here), write (expr,), like in Python. — phipsgabler

phipsgabler phipsgabler · Accepted Answer · 2019-01-22T09:22:26

Your are never actually calling the inner constructor in Coords(). To achieve what you want:

XYZ() = XYZ(rand(), rand(), rand())
Coords() = Coords([XYZ() for _ in 1:10])

But I would recommend against providing a constructor that initializes a special random layout. Instead, you could properly overload rand for XYZ, which gives you an array-rand for free:

julia> import Random

julia> Random.rand(rng::Random.AbstractRNG, ::Random.SamplerType{XYZ}) = XYZ(rand(rng), rand(rng), rand(rng))

julia> rand(XYZ)
XYZ(0.7580070440261963, 0.15662533181464178, 0.7450476071687568)

julia> rand(XYZ, 10)
10-element Array{XYZ,1}:
 XYZ(0.5984858021544213, 0.16235318543392796, 0.729919026616209)  
 XYZ(0.45516751074248374, 0.9667694185826785, 0.39798147467761247)
 XYZ(0.7329129925610325, 0.7725520616259764, 0.42264014343531)    
 XYZ(0.10415869248789567, 0.4193162272272648, 0.3265074454289505) 
 XYZ(0.2286383169588948, 0.7119393337105202, 0.5166340562764509)  
 XYZ(0.23011692279595186, 0.35344093654843767, 0.9488399720160021)
 XYZ(0.20464532213275577, 0.05761320898130973, 0.7694525743407523)
 XYZ(0.3022492318001946, 0.9212313012991236, 0.819167833632835)   
 XYZ(0.6331585756351794, 0.9812979781832118, 0.3969247687412505)  
 XYZ(0.6049257667248391, 0.7155977104637223, 0.5294492917395452)  

julia> Coords(rand(XYZ, 10))
Coords(XYZ[XYZ(0.633945, 0.882152, 0.750866), XYZ(0.496134, 0.241877, 0.188791), XYZ(0.267383, 0.552298, 0.613393), XYZ(0.569428, 0.503757, 0.120985), XYZ(0.822557, 0.982106, 0.37321), XYZ(0.250684, 0.701853, 0.509496), XYZ(0.886511, 0.83301, 0.381657), XYZ(0.628089, 0.00574949, 0.730268), XYZ(0.382186, 0.411701, 0.86016), XYZ(0.904469, 0.854098, 0.270464)])

Accessing array inside composite type in Julia

1 Answers