How to accomplish `[x*y for x in 1:y, y in 1:5]`?

New to Julia
1

How can I make a nested list comprehension where the inner iterator depends on the outer one?

Using a for loop, I can do

res = []
for y in 1:5, x in 1:y
    push!(res, x*y)
end

but I would like to accomplish the same using an expression like [x*y for x in 1:y, y in 1:5], if possible.

Edit: I just figured out

vcat([[x*y for x in 1:y] for y in 1:5]...)

although my understanding is that splatting is to be avoided if possible.

1 Like
2

This gives the same result

[x*y for y in 1:5 for x in 1:y]

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3

Thank you. I was stuck because I didn’t expect to have to move the inner iterator to the outside.

I guess the justification for this design is that this puts the x and y iterators in the same order as the equivalent for loop. Is this compatibility principle consistent across languages? I checked and Python works like Julia in this regard:

In [2]: [x*y for y in range(5) for x in range(y)]
Out[2]: [0, 0, 2, 0, 3, 6, 0, 4, 8, 12]
1 Like