CODEWITHSUNDEEP
sortingelixirlist-comprehension
smkarber
smkarber

Reputation: 607

Elixir how do you sort a list comprehension?

I have been struggling with sorting this list comprehension for a while now, and I don't understand two specific things about it.

for x <- span(2, n), y <- span(2, n), x <= y, x * y <= n, into: [], do: x * y

What it does is create a list of all non-primes up to n. Now if I try:

for x <- span(2, n), y <- span(2, n), x <= y, x * y <= n, into: [], do: x * y
  |> Enum.sort


for x <- span(2, n), y <- span(2, n), x <= y, x * y <= n, into: [], do: x * y   
  |> Enum.sort()

Both methods give me the error:

protocol Enumerable not implemented for 4

So my first question is how do you sort a comprehension using pipes?

EDIT:: Removed due to duplicates being present and my not noticing them =>

If I try:

comps = for x <- span(2, n), y <- span(2, n), x <= y, x * y <= n, into: [], do: x * y
Enum.sort(comps)

The list is sorted, but now it shows duplicates in the list. My second question is why does the output of the comprehension contain duplicates if I store it in a variable and not contain them otherwise?

That seems like a rather arbitrary interaction.

Upvotes: 2

Views: 745

Answers (1)

smkarber
smkarber

Reputation: 607

Upon further reading, the solution is to encompass the comprehension in parentheses before piping.

(for x <- span(2, n), y <- span(2, n), x <= y, x * y <= n, into: [], do: x * y)
  |> Enum.sort

The above code is the solution. Parentheses are not needed when piping comprehensions in block format, but inline comprehensions require parentheses.

I discovered this by reading: Elixir: error when piping to a function the result of inline comprehension

I did not discover this question prior to my posting although I searched Elixir comprehension, as I was not aware of the term 'inline comprehension'.

Upvotes: 4

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