Creating sublists in a for comprehension

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}], [{2,1}, {2,2}, {2,3}], [{3,1}, {3,2}, {3,3}]]

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

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.

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

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