Strange Output When Filtering List with `Enum.filter/2`

Questions / Help
, ,
1

I’m encountering a strange issue when using Enum.filter/2 in my Elixir script. The problem occurs when I filter a list with a condition that elements should be greater than a certain value using pipe operator.

pipe_operator.exs

defmodule PipeOperator do
  def return_big(list) do
    list
    |> Enum.map(&(&1 * 2))
    |> Enum.filter(&(&1 > 40))
  end
end

big = PipeOperator.return_big([2, 5, 20, 30,40])
IO.inspect(big)

EXPECTED RESULT
I expect the output to be a list of elements greater than 40 after they have been doubled. For the input list [2,5,20,30,40] . The doubled list is [4,10,40,60,80] and the filtered list should be [60,80].

ACTUAL RESULT
When I filter with &(&1 > 40), instead of the expected list, I get this strange output in my terminal:

myname@Lenovo-V14-IGL:~/Desktop/learnelixir/modules$ elixir pipe_operator.exs 
~c"<P"
myname@Lenovo-V14-IGL:~/Desktop/learnelixir/modules$

and sometime ~c"<Px" , ~c"<\n(<Pdepending the value of list.

However, if I change the filter condition to &(&1 > 2), or 1 it works as expected, and I get the correct filtered list.

Elixir version : Elixir 1.17.0 (compiled with Erlang/OTP 27)
OS : Linux mint 21.2

2

IO.inspect is interpreting the list of integers as a Charlist, and rendering it with the ~c sigil. You can explicitly tell IO.inspect to render the list of integers as a list.

See: FAQ · elixir-lang/elixir Wiki · GitHub

iex(6)> IO.inspect([60,80])
~c"<P"
~c"<P"
iex(7)> IO.inspect([60,80], charlists: :as_lists)
[60, 80]
~c"<P"
1 Like
3

They are exactly the same, the numbers can be interpreted as printable characters so they are shown as such. This setting can be disabled btw.