List to Keyword List in Elixir

Question

I have a list of results that I pulled in using Ecto. I want to end up with a keyword list that I can then use to populate a <select> inside of Phoenix but I'm unsure how to turn this list into a keyword list like ["1": "Author #1", "2": "Author #2"]

authors = Repo.all(Author)
# How would I create ["1": "Author #1", "2": "Author #2"]

Answer 1

A keyword list expects atoms as keys. The good news is that you don't need a keyword list to give to select. Here are two approaches:

1. Do it directly in the query:

   authors = Repo.all from a in Author, select: {a.name, a.id}
   

2. Do it on the data:

   authors = Repo.all Author
   Enum.map(authors, fn a -> {a.name, a.id} end)
   

The advantage of the first one is that you will load only the data you need from the table.

Answer 2

Select just the author names using Enum.map

authorNames = authors |> Enum.map(fn a-> a.name end)

then use Enum.zip to setup the key value pairs

1..Enum.count(authors ) |> Enum.map(fn x-> to_string(x) end) |> Enum.zip(authorNames)

this will produce soemthing like:

[{"1", "Author #1"}, {"2", "Author #2"}]

If you want it to be a true keyword list you need the first element to be a atom because keyword lists only use atoms as keys

1..Enum.count(authors ) |> Enum.map(fn x-> x |> to_string |> String.to_atom end) |> Enum.zip(authorNames)

which will produce

["1": "Author #1", "2": "Author #2"]

But I've always heard to manage the number of atoms you have carefully and that converting large number of strings to atoms isn't a best practice. Unless you know how many authors your query will return you may need to be careful when converting the key numbers to atoms.