Is there a simple way to create a struct with fields, e.g.
struct Test{T}
dt
v
z
end
function Test(
f::Vector,
dt = zeros(Float32, length(f)),
v = ones(Int64, length(f)),
z = zeros(Float32, length(f) + 1)
)
Test{eltype(dt)}(dt, v, z)
end
And then use these fields in a downstream function without allocating arrays? e.g.
function transform(f::Vector{T}, tfm::Test) where {T}
dt = tfm.dt
v = tfm.v
z = tfm.z
...
end
My original function which didn't utilize any custom types doesn't allocate anything but when trying to use my Test
type I can't figure out how to avoid allocations
tfm = Test(f)
@benchmark transform($f, $tfm)
# returns
Memory estimate: 224 bytes, allocs estimate: 14.
@benchmark transform($f, $dt, $v, $z)
# returns
Memory estimate: 0 bytes, allocs estimate: 0.
https://docs.julialang.org/en/v1/manual/performance-tips/#Avoid-fields-with-abstract-type
Thank you! That is useful but I don't think it solved my problem of allocating arrays. Any idea how I might pre-allocate the arrays in the Test
function
struct Test{T <: AbstractArray} <: DistanceTransform
dt::T
v::T
z::T
end
function Test(
f::Vector,
dt = zeros(Float32, length(f)),
v = ones(Int64, length(f)),
z = zeros(Float32, length(f) + 1)
)
Test{AbstractArray}(dt, v, z)
end
In order to avoid allocations in the transform
operation?
function transform(f::Vector{T}, tfm::Test) where {T}
dt = tfm.dt
v = tfm.v
z = tfm.z
...
end
Do you mean that you want to keep reusing the same existing arrays in the Test constructor instead of allocating new arrays for every instance of Test?
I think so..
I don't really understand types yet so I might be confused, but yes I think that is what I want
Hmm, I don't mean to be rude, but I suggest not doing optimizations until you know you have a problem. E.g. if you re-use the same arrays for different Test objects, you could run into some annoying bugs if the arrays are modified and you forget different Test objects share the same arrays
But you said the transform function allocated. The part of the function you posted should not allocate, so if that function has a problem, it must be in the omitted part
That makes sense. I am attempting this in order to learn Julia better. It might also add some convenience in the future, but it might be too much of a headache.
The basic function that I am attempting to recreate is non-allocating like so:
f = [1, 0, 1, 0]
dt = zeros(Float32, length(f))
v = ones(Int64, length(f))
z = zeros(Float32, length(f) + 1)
function squared_euclidean_distance_transform(f::AbstractArray{T,1}, dt, v, z) where {T}
n = length(f)
k = 1
z[1] = -Inf32
z[2] = Inf32
# Lower envelope operation
for q in 2:n
while true
s = ((f[q] + q^2) - (f[v[k]] + v[k]^2)) / (2 * q - 2 * v[k])
if s ≤ z[k]
k -= 1
else
k += 1
v[k] = q
z[k] = s
z[k + 1] = Inf32
break
end
end
end
# Distance transform operation
k = 1
for q in 1:n
while z[k + 1] < q
k = k + 1
end
dt[q] = (q - v[k])^2 + f[v[k]]
end
return dt
end
@benchmark squared_euclidean_distance_transform($f, $dt, $v, $z)
# returns
Memory estimate: 0 bytes, allocs estimate: 0.
Ahhh - the issue before was simply that the parameter of Test was AbstractArray - which means the fields were abstractly typed
For the code to be efficient (and non-allocating), you need to be able to predict the type of each field only from the type of the Test object itself
Thank you! That is useful but I don't think it solved my problem of allocating arrays
Like Jakob mentioned, you want to do Test{typeof(dt)}(dt, v, z)
instead of Test{AbstractArray}(dt, v, z)
. Or even better just do Test(dt, v, z)
.
Does this work when you need each field to be a different type? I am getting some errors from both Test{typeof(dt)}(dt, v, z)
and Test(dt, v, z)
Probably that's because you defined all fields as having the same type.
You should do something like this
struct Test{T1 <: AbstractArray, T2 <: AbstractArray} <: DistanceTransform
dt::T1
v::T2
z::T1
end
and use Test(dt, v, z)
form to initialize it, since compiler can infer types on its own.
By the way, you can use AbstractVector{T}
alias instead of AbstractArray{T, 1}
. It's more straightforward.
Thank you! One more thing, if I want to dispatch on the type of f
how would I do that in the initialization function? The code below works, if I want to restrict f::Vector{Int64}
or img::Matrix{Int64}
but I run into errors when I try to allow more flexibility e.g. f::Vector{Number}
function Test(
f::Vector{Int64},
dt = zeros(Float32, length(f)),
v = ones(Int64, length(f)),
z = zeros(Float32, length(f) + 1)
)
Test(dt, v, z)
end
function Test(
img::Matrix{Int64},
dt = zeros(Float32, size(img)),
v = ones(Int64, size(img)),
z = zeros(Float32, size(img) .+ 1)
)
Test(dt, v, z)
end
What kind of errors and how more general definition looks like?
function Test(
f::Vector,
dt = zeros(Float32, length(f)),
v = ones(Int64, length(f)),
z = zeros(Float32, length(f) + 1)
)
Test(dt, v, z)
end
function Test(
f::Vector{Number},
dt = zeros(Float32, length(f)),
v = ones(Int64, length(f)),
z = zeros(Float32, length(f) + 1)
)
Test(dt, v, z)
end
f = [1, 0, 1, 0]
tfm = Test(f)
tfm
MethodError: no method matching Main.workspace134.Test(::Vector{Int64})
Closest candidates are:
Main.workspace134.Test(::T1, !Matched::T2, !Matched::T1) where {T1<:AbstractArray, T2<:AbstractArray} at /Users/daleblack/Google Drive/dev/julia/pluto notebooks/restructure_distance_transforms.jl#==#95897bab-7702-48e7-8e0d-b5c0c83d4d94:3
Main.workspace134.Test(!Matched::Vector{Number}) at /Users/daleblack/Google Drive/dev/julia/pluto notebooks/restructure_distance_transforms.jl#==#95897bab-7702-48e7-8e0d-b5c0c83d4d94:8
Main.workspace134.Test(!Matched::Vector{Number}, !Matched::Any) at /Users/daleblack/Google Drive/dev/julia/pluto notebooks/restructure_distance_transforms.jl#==#95897bab-7702-48e7-8e0d-b5c0c83d4d94:8
...
top-level scope@Local: 1[inlined]
I'm using Pluto btw in case that matters
You hit a classical beginner mistake in Julia: Vector{Int} is not a subtype of Vector{Number}. That is, if A is a subtype of B, that does NOT mean that T{A} is a subtype of T{B}
For that, you would need to write Vector{<: Number}.
Hmm there is still a problem
struct Test{T1 <: AbstractArray, T2 <: AbstractArray} <: DistanceTransform
dt::T1
v::T2
z::T1
end
function Test(
f::Vector{<: Real},
dt = zeros(Float32, length(f)),
v = ones(Int64, length(f)),
z = zeros(Float32, length(f) + 1)
)
Test(dt, v, z)
end
function Test(
img::Array{<: Real},
dt = zeros(Float32, size(img)),
v = ones(Int64, size(img)),
z = zeros(Float32, size(img) .+ 1)
)
Test(dt, v, z)
end
tfm = SquaredEuclidean(f)
tfm
MethodError: Main.workspace162.Test(::Vector{Float32}, ::Vector{Int64}, ::Vector{Float32}) is ambiguous. Candidates:
Main.workspace162.Test(dt::T1, v::T2, z::T1) where {T1<:AbstractArray, T2<:AbstractArray} in Main.workspace162 at /Users/daleblack/Google Drive/dev/julia/pluto notebooks/restructure_distance_transforms.jl#==#95897bab-7702-48e7-8e0d-b5c0c83d4d94:3
Main.workspace162.Test(f::Vector{var"#s1108"} where var"#s1108"<:Real, dt, v) in Main.workspace162 at /Users/daleblack/Google Drive/dev/julia/pluto notebooks/restructure_distance_transforms.jl#==#95897bab-7702-48e7-8e0d-b5c0c83d4d94:8
Main.workspace162.Test(img::Array{var"#s1112", N} where {var"#s1112"<:Real, N}, dt, v) in Main.workspace162 at /Users/daleblack/Google Drive/dev/julia/pluto notebooks/restructure_distance_transforms.jl#==#95897bab-7702-48e7-8e0d-b5c0c83d4d94:18
Possible fix, define
Main.workspace162.Test(::T1, ::T2, ::T1) where {T1<:(Vector{var"#s1108"} where var"#s1108"<:Real), T2<:AbstractArray}
Main.workspace162.Test(::Vector{Float32}, ::Vector{Float32}, ::Vector{Int64}, ::Vector{Float32})@Other: 15
top-level scope@Local: 1[inlined]
At this point you have introduced too many functions, best thing you can do is to restart Julia.
But I can't understand, what is the difference between all these methods, they all create the same object. You do not use type information at all, so you can for example define
function Test(
img::AbstractArray,
dt = zeros(Float32, size(img)),
v = ones(Int64, size(img)),
z = zeros(Float32, size(img) .+ 1)
)
Test(dt, v, z)
end
This definition will work for vectors and matrices, and for any type of elements.
There is no need to over constrain.
Yeah, great point. AbstractArray
covers all that I need
Thank you for all the help everyone!
Dale Black has marked this topic as resolved.
Last updated: Nov 06 2024 at 04:40 UTC