julia> A = [2, 2, 2] 3-element Vector{Int64}: 2 2 2 julia> all(A, dims = 1) 1-element Vector{Bool}: 0 Why does this code return 0, not 1?

In Julia unlike python for example values are not considered truthy. See a discussion about this concept here: On the arbitrariness of truth(iness) . If you would like to test whether all values are nonzero for example you could provide a function to the all function: julia> all(!iszero, [2,2,2], d…

Thanks, but why does this code return 1? julia> all([3, 3, 3], dims = 1) 1-element Vector{Bool}: 1

julia> for i in 0:10 A = i * ones(Int, 3) @show all(A, dims = 1) end all(A, dims = 1) = Bool[0] all(A, dims = 1) = Bool[1] all(A, dims = 1) = Bool[0] all(A, dims = 1) = Bool[1] all(A, dims = 1) = Bool[0] all(A, dims = 1) = Bool[1] all(A, dims = 1) = Bool[0] all(A, dims =…

Wow, that’s wild. Looks like a bug to me. This should probably just error, like it does without the dims keyword argument: all([1, 1, 1]) ERROR: TypeError: non-boolean (Int64) used in boolean context Stacktrace: [1] _all @ .\reduce.jl:1161 [inlined] [2] _all @ .\reducedim.jl:903 [inlined] …

Related: julia> any([1, 2], dims=1) ERROR: InexactError: Bool(3) Like, I guess it’s good that it gives an error, but it’s not really the right error.

[image] pfitzseb: This boils down to julia> mapreduce(identity, &, [3,3,3]; dims=1) Could you provide some tips how to get there? Thanks.

@edit all([3, 3, 3], dims = 1) and scroll down to $(_fname)(f, A, dims; kw...) = mapreduce(f, $(op), A; dims=dims, kw...) You could also @enter all([3, 3, 3], dims = 1) (in VS Code or with Debugger.jl loaded) and then step around a bit until you end up in that function (which may be annoying becau…

Thanks Sebastian. And sorry, my brain is overheating: I cannot see the connection between “all vector elements being true” and that unfamiliar mapreduce expression. (if all vector elements are booleans, it is a bit more easy to see)

Well, any(x) == mapreduce(is_truthy, |, x) == is_truthy(x[1]) | is_truthy(x[2]) | ... | is_truthy(x[end]) all(x) == mapreduce(is_truthy, &, x) == is_truthy(x[1]) & is_truthy(x[2]) & ... & is_truthy(x[end]) For booleans, is_truthy == identity. This of course breaks down when the eltype of x is e.g.…

What does this result mean?

General Usage

pfitzseb June 2, 2022, 3:28pm 6

This boils down to

julia> mapreduce(identity, &, [3,3,3]; dims=1)
1-element Vector{Bool}:
 1

julia> mapreduce(identity, &, [2,2,2]; dims=1)
1-element Vector{Bool}:
 0

and definitely is a bug.

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What does this result mean?

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