Hello all, I’m going through the open source beta version of the Dockyard Academy curriculum ( GitHub - DockYard-Academy/curriculum · GitHub ) and I’m doing some exercises about for comprehensions. In one of these exercises I have to convert the following nested Enum.map into a comprehension with th…

I believe you need multiple comprehensions. for a <- 1..3 do a end |> IO.inspect # [1,2,3] for a <- 1..3, b <-1..3 do {a,b} end |> IO.inspect #[{1,1}, {1,2}, {1,3}, {2,1}, {2,2}, {2,3}, {3,1}, {3,2}, {3,3}] for a <-1..3 do for b <- 1..3 do {a,b} end end |> IO.inspect # [[{1,1}, {1,2}, {1,3}], [{2…

I think this can be done with only two generators (mental mapping: 1 map = 1 for, nested map = nested for), I wonder how can one convert those two maps into three for-s?

Thank you for the answers! I did not even think about the possibility of nesting the for’s, so I learned something new :grinning: I still wonder how it can be done with three generators in one comprehension, like they asked. Is it even possible?

[image] jschepmans: I still wonder how it can be done with three generators in one comprehension, like they asked. Is it even possible? I don’t think so, seems to be an error.

I think it is possible with a for reduce You can build the tuples from b,c and depending on the value of a push it to an accumulator that starts with [,,]

You are right, it can absolutely be possible with a for with reduce and two “zipped” fors as given originally. I always forget the existence of the reduce option of for comprehensions.

Is for..reduce not a generator?

The a <- list part of for is called a generator if one wants to be correct. Doesn’t matter if there’s a reduce or not.

yeah I had to look up the definition of generator. I am embarrassed to admit that I didn’t know what a generator meant in Elixir until now. So TIL :slight_smile:

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Creating sublists in a for comprehension

Questions & Help Questions

adamu December 17, 2022, 3:39pm 8

Reduce is not a generator, that would still only be two generators.