groups maps by common keys

main.exs

list = [
  %{id: 1, k: "k1", name: "name a", text: "text a"},
  %{id: 1, k: "k1", name: "name b", other: "other b"},
  %{id: 1, k: "k2", name: "name k2", other: "other k2"}
]

keys = [:id, :k]

list
|> Enum.group_by(&Map.take(&1, keys))
|> Enum.map(fn {common, others} ->
  others
  |> Enum.reduce(%{}, fn data, acc ->
    Enum.reduce(data, acc, fn {k, v}, acc ->
      case acc do
        %{^k => vs} -> %{acc | k => [v | vs]}
        acc -> Map.put(acc, k, [v])
      end
    end)
  end)
  |> Map.merge(common)
end)

_output = """
[
  %{id: 1, k: "k1", name: ["name b", "name a"], other: ["other b"], text: ["text a"]},
  %{id: 1, k: "k2", name: ["name k2"], other: ["other k2"]}
]
"""