Spanning repeatable keys - functional-programming

Question

from such:
[
{"Caerus1", "Ramses Refiner"},
{"Caerus1", "Jupiter Refiner"},
{"Caerus1", "Jupiter Other"},
{"Caerus1", "Trader 13"},
{"Caerus1", "Cathode Supplier 4"},
{"Dionysus3", "Cathode Supplier 4"},
{"Dionysus3", "Ramses Refiner"},
{"Dionysus3", "Trader 13"},
{"Dionysus3", "Jupiter Refiner"},
{"Dionysus3", "Jupiter Other"},
{"Prometheus2", "Jupiter Other"},
{"Prometheus2", "Ramses Refiner"},
{"Prometheus2", "Trader 13"},
{"Prometheus2", "Cathode Supplier 4"},
{"Prometheus2", "Jupiter Refiner"}
]
I'd like to achieve this:
[
{"Caerus1" => ["Ramses Refiner", "Jupiter Refiner", "Jupiter Other", "Trader 13", "Cathode Supplier 4"]},
.
.
.
]
So basically converting these tuples into a map with unique key - so it doesn't repeat (that I can do easily) the hard part is making a list of the 2nd element strings.
Thanks in advance

Answer 1

1> L_tup = [
1> {"Caerus1", "Ramses Refiner"},
1> {"Caerus1", "Jupiter Refiner"},
1> {"Caerus1", "Jupiter Other"},
1> {"Caerus1", "Trader 13"},
1> {"Caerus1", "Cathode Supplier 4"},
1> {"Dionysus3", "Cathode Supplier 4"},
1> {"Dionysus3", "Ramses Refiner"},
1> {"Dionysus3", "Trader 13"},
1> {"Dionysus3", "Jupiter Refiner"},
1> {"Dionysus3", "Jupiter Other"},
1> {"Prometheus2", "Jupiter Other"},
1> {"Prometheus2", "Ramses Refiner"},
1> {"Prometheus2", "Trader 13"},
1> {"Prometheus2", "Cathode Supplier 4"},
1> {"Prometheus2", "Jupiter Refiner"}
1> ].
[{"Caerus1","Ramses Refiner"},
{"Caerus1","Jupiter Refiner"},
{"Caerus1","Jupiter Other"},
{"Caerus1","Trader 13"},
{"Caerus1","Cathode Supplier 4"},
{"Dionysus3","Cathode Supplier 4"},
{"Dionysus3","Ramses Refiner"},
{"Dionysus3","Trader 13"},
{"Dionysus3","Jupiter Refiner"},
{"Dionysus3","Jupiter Other"},
{"Prometheus2","Jupiter Other"},
{"Prometheus2","Ramses Refiner"},
{"Prometheus2","Trader 13"},
{"Prometheus2","Cathode Supplier 4"},
{"Prometheus2","Jupiter Refiner"}]
2> F = fun({K,V},Acc) ->
2> case Acc of
2> [#{K:=L}|T] -> [#{K=>[V|L]}|T];
2> Acc -> [#{K => [V]}|Acc]
2> end
2> end.
#Fun<erl_eval.43.79398840>
3> lists:foldl(F,[],L_tup).
[#{"Prometheus2" =>
["Jupiter Refiner","Cathode Supplier 4","Trader 13",
"Ramses Refiner","Jupiter Other"]},
#{"Dionysus3" =>
["Jupiter Other","Jupiter Refiner","Trader 13",
"Ramses Refiner","Cathode Supplier 4"]},
#{"Caerus1" =>
["Cathode Supplier 4","Trader 13","Jupiter Other",
"Jupiter Refiner","Ramses Refiner"]}]
4>
if the initial list L_tup is not sorted it is necessary to use lists:sort(L_tup).
The former code will have a result looking like the example you give: a list of map. But it is not a map as described in the last sentence. To create a map you can use the next code (this version does not need a sorted input):
4> F1 = fun({K,V},M) ->
4> L = maps:get(K,M,[]),
4> M#{K=>[V|L]}
4> end.
#Fun<erl_eval.43.79398840>
5> lists:foldl(F1,#{},L_tup).
#{"Caerus1" =>
["Cathode Supplier 4","Trader 13","Jupiter Other",
"Jupiter Refiner","Ramses Refiner"],
"Dionysus3" =>
["Jupiter Other","Jupiter Refiner","Trader 13",
"Ramses Refiner","Cathode Supplier 4"],
"Prometheus2" =>
["Jupiter Refiner","Cathode Supplier 4","Trader 13",
"Ramses Refiner","Jupiter Other"]}
6> % could be written in a single line :o)
6> % lists:foldl(fun({K,V},M) -> M#{K=>[V|maps:get(K,M,[])]} end,#{},L_tup).

Answer 2

In Elixir it's quite easy with Enum.group_by/3:
iex> Enum.group_by(values, fn {key, _} -> key end, fn {_, value} -> value end)
%{
"Caerus1" => ["Ramses Refiner", "Jupiter Refiner", "Jupiter Other",
"Trader 13", "Cathode Supplier 4"],
"Dionysus3" => ["Cathode Supplier 4", "Ramses Refiner", "Trader 13",
"Jupiter Refiner", "Jupiter Other"],
"Prometheus2" => ["Jupiter Other", "Ramses Refiner", "Trader 13",
"Cathode Supplier 4", "Jupiter Refiner"]
}