How to best iterate over k-dimensional collection, e.g. (n,k) matrix?

New to Julia
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These are the most idiomatic ways, I think:

julia> a = [ 1 2 3; 4 5 6 ]
2×3 Matrix{Int64}:
 1  2  3
 4  5  6

julia> for i in axes(a,2), j in axes(a,1)
           @show j, i, a[j,i]
       end
(j, i, a[j, i]) = (1, 1, 1)
(j, i, a[j, i]) = (2, 1, 4)
(j, i, a[j, i]) = (1, 2, 2)
(j, i, a[j, i]) = (2, 2, 5)
(j, i, a[j, i]) = (1, 3, 3)
(j, i, a[j, i]) = (2, 3, 6)

julia> for c in CartesianIndices(a)
           @show c[1], c[2], a[c]
       end
(c[1], c[2], a[c]) = (1, 1, 1)
(c[1], c[2], a[c]) = (2, 1, 4)
(c[1], c[2], a[c]) = (1, 2, 2)
(c[1], c[2], a[c]) = (2, 2, 5)
(c[1], c[2], a[c]) = (1, 3, 3)
(c[1], c[2], a[c]) = (2, 3, 6)

There is nothing wrong with your double loop, just be sure that the indexes are inbounds (something that is guaranteed by these alternatives)

ps: a matrix is definitely ok. Alternatively you may want to look at DataFrames package and companions, if you want something more sophisticated in terms of data manipulation.

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