czrpb
ARRG! Still stuck in the imperative world! Help! :)
Have a Map whose values are MapSets: Best way to update?
Currently have:
keys
|> Enum.reduce(
%{},
fn key, acc ->
acc
|> Map.put(
key,
Map.get(acc, key, MapSet.new())
|> MapSet.put(get_value_to_add(key))
)
end
)Marked As Solved
kokolegorille
Except the MapSet…
iex> list = ["apple", "apricot", "banana", "blueberry", "kiwi", "blackberry"]
["apple", "apricot", "banana", "blueberry", "kiwi", "blackberry"]
iex> Enum.group_by(list, &String.first/1)
%{
"a" => ["apple", "apricot"],
"b" => ["banana", "blueberry", "blackberry"],
"k" => ["kiwi"]
}
With MapSet…
list
|> Enum.group_by(&String.first/1)
|> Enum.reduce(%{}, fn {k, v}, acc -> Map.put(acc, k, MapSet.new(v)) end)
%{
"a" => #MapSet<["apple", "apricot"]>,
"b" => #MapSet<["banana", "blackberry", "blueberry"]>,
"k" => #MapSet<["kiwi"]>
}
With MapSet, short version 
iex> list
|> Enum.group_by(&String.first/1)
|> Enum.reduce(%{}, &Map.put(&2, elem(&1, 0), MapSet.new(elem(&1, 1))))
%{
"a" => #MapSet<["apple", "apricot"]>,
"b" => #MapSet<["banana", "blackberry", "blueberry"]>,
"k" => #MapSet<["kiwi"]>
}
Also Liked
kokolegorille
At least here I prefer … MapSet.new(value) 
kokolegorille
That applies here too.
You could use…
|> Map.new()
…instead
al2o3cr
Could alternatively be spelled:
update_in acc, [Access.key(key, MapSet.new())], &MapSet.put(&1, get_value_to_add(key))
ityonemo
There’s a limit to how much I’m willing to let my code look like it’s object oriented 
kokolegorille
It is not very clear what You want to achieve… better put some data and expected result.
Anyway, this looks wrong (bad parens placement…)
Map.get(acc, key, MapSet.new())
|> MapSet.put(get_value_to_add(key))
and piping once is something I try not to do. At least two pipes, otherwise I pass the parameter normally.
There is a Map.update function
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