(FunctionClauseError) no function clause matching in Access.get/3 - separate question because additional ones in the topic are being deleted

Question

Problem no. 1 why my additional question in (FunctionClauseError) no function clause matching in Access.get/3 was deleted by moderator whereas it was asking a question about the answer to the original quesiton

Problem no. 2 I am trying to comprehend why: the original and (NOT working) answer

{:ok, decode_csv} =
  File.stream!('users_departs.csv')
  |> Stream.drop(1)
  |> CSV.decode(headers: [:name, :title, :departments])

raises:

== Compilation error in file lib/data_dictionary.ex ==
** (MatchError) no match of right hand side value: #Function<62.51129937/2 in Stream.transform/3>
...

The documentation is extremely vague on this and I am unlucky enough to have just upgraded to the 2.2.1 version of the CSV.

I am quite puzzled not knowing how the heck process the return value of the CSV.decode...

With my best wishes Tomasz

Answer 1

As clearly stated in the documentation, CSV.decode/2 returns a stream . Until you have it terminated, it's a stream. That said, what you need is to ensure you a) terminate it somehow, eg by converting to the list with Enum.to_list/1 , and b) you properly handle the return values, which are basically tuples {:ok, values} or {:error, description} .

For the trivial case, when you are fine with raising on errors, just use the banged version CSV.decode!/2 which returns a streamed list or raises if it fails to parse any row.

'users_departs.csv'
|> File.stream!()
|> Stream.drop(1)
|> CSV.decode!(headers: [:name, :title, :departments])
|> Enum.to_list() # ESSENTIAL!