James Wrigley (Aug 04 2022 at 14:47): James Wrigley (Aug 04 2022 at 14:47):From the docs my understanding is that Arrays of optionally missing values actually store two arrays, one for the data and one to store whether or not the value is missing. If I've got that right, I don't understand why sizeof() says these are the same size in memory:
julia> x = rand(UInt16, 2, 2)
2×2 Matrix{UInt16}:
61892 4489
19311 27433
julia> y = Array{Union{Missing, UInt16}}(missing, 2, 2)
2×2 Matrix{Union{Missing, UInt16}}:
missing missing
missing missing
julia> sizeof(x)
8
julia> sizeof(y)
8
Shouldn't sizeof(y) == 12? 8 bytes for the data plus 4 bytes for the mask.
James Wrigley (Aug 04 2022 at 14:53):Ah hah, turns out I should be using Base.summarysize(): https://discourse.julialang.org/t/sizeof-vector-union-missing-t-and-hypothetical-size/15271/14
julia> Base.summarysize(x)
48
julia> Base.summarysize(y)
52
Last updated: Nov 07 2025 at 04:42 UTC