Example: julia> A = fill(fill(0,2), 3) 3-element Vector{Vector{Int64}}: [0, 0] [0, 0] [0, 0] julia> A[1][2] = 5 5 julia> A 3-element Vector{Vector{Int64}}: [0, 5] [0, 5] [0, 5] The result is not what I would expect. Instead, I would have expected to get julia> A 3-element Vector{Vector{I…

Ah yeah this tripped me up at first as well. If you look at the help page for fill: help?> fill If x is an object reference, all elements will refer to the same object: julia> A = fill(zeros(2), 2); julia> A[1][1] = 42; # modifies both A[1][1] and A[2][1] julia> A 2-element Vector{V…

Another data point. When the vectors are different sizes, then I get the behavior I expect: julia> A = [[0,1], [2,3,4], [5,6]] 3-element Array{Array{Int64,1},1}: [0, 1] [2, 3, 4] [5, 6] julia> A[1][2] = 10 10 julia> A 3-element Array{Array{Int64,1},1}: [0, 10] [2, 3, 4] [5, 6]

Thanks for the help! I guess I was confused because it didn’t occur to me that the internal fill(0,2) would be creating a new object that persists. I would have realized what’s happening if I had written this instead: julia> b = fill(0,2) 2-element Array{Int64,1}: 0 0 julia> A = fill(b, 3) 3-el…

I think this is a really important thing for people to come to Julia (especially from R) to realize. In Julia, whenever you call f(g(x)) f only sees the result of g(x), not how it got there. This is why macros have special syntax. In R, all functions are the equivalent of macros in Julia, which add…

@Oscar_Smith , could you please explain a bit further what this fill()'s behavior has to do with f(g(x)), and why this is the most logical choice? It looks like another trap that is very easy to fall into. Thanks. A = fill([0,0], 3) A[1][2] = 5 julia> A 3-element Vector{Vector{Int64}}: [0, 5] [0,…

First, if all you want is a matrix, then fill(0, (2, 3)) suits your need. If you really want an array of arrays, then you have to create independent arrays for each entry in the larger array (usually with list comprehension). For your question, fill([1], 3) could be interpreted as such: create a…

I agree that the behavior of fill([0, 0], 2) is counterintuitive and kind of pointless. This question comes up on a regular basis here on Discourse. I would favor changing this behavior for Julia 2.0.

I just opened an issue that suggests changing the fill behavior for Julia version 2.0. https://github.com/JuliaLang/julia/issues/41209

What is going on here? julia> a=fill(zeros(2),2) 2-element Vector{Vector{Float64}}: [0.0, 0.0] [0.0, 0.0] julia> a[1]=[1,1] 2-element Vector{Int64}: 1 1 julia> a 2-element Vector{Vector{Float64}}: [1.0, 1.0] [0.0, 0.0] What is going on here? Why didn’t I get: [1.0, 1.0] [1.0, 1.0] ?

[image] blackeneth: What is going on here? a = fill(zeros(2), 2) this creates a 2-element vector, where both elements refer to the same object, namely the newly created zeros(2). i.e. a[1] refers to the same object as a[2]. This is the behaviour of fill. If you modify (mutate) that object,…

Simple question about assignment to a vector of vectors

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Paul_Soderlind June 12, 2021, 12:16pm 8

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Simple question about assignment to a vector of vectors

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