Statement mindset:
Expression mindset:
Statements don’t work in an expression based language - that’s why.
peerreynders
9mm
I’m more referring to all the errors for everything I try to do, and weird unexpected things (which is normal of course). Not complaining, just saying… brutal
0
9mm
Thats awesome, I like that 1 line if, and good point about the variable name.
I take it :maps is straight erlang?
0
Eiji
Yes this comes from Erlang. Enum module always returns List. Of course you can do Enum.into(updated_data, %{}), but this makes no sense if you can directly work on Map instead.
1
9mm
This is a dumb question, but why don’t they have a filter function which returns a map? I feel like that would be a common task?
0
Eiji
Enum is protocol which Map (of course not only) implements, but this means it would return List in (unified) result unless you would not turn it into Map again.
So no matter if you pass List or Map it would always return List. Also when you are returning Tuple (i.e. {key, value}) and collect results then you got List of Tuple (like [{key, value}]) i.e. Keyword (which needs atom as key for example: [a: 5] is [{:a, 5}] nicely printed) which is just List. It’s why typical Map manipulation returns List.
Not sure how Erlang solves it - not even sure which one is faster or slower, but Erlang way is definitely easier to read for me since we have less code.
The only different thing is Enum.reduce/3 which acc (2nd argument is initial value) could be any term and we work directly on it, so instead return Tuple (again {key, value}) we are returning updated version of acc which does not chances its type unless we decide to do so.
1
cmkarlsson
Pretty basic implementation:
filter(Pred,Map) when is_function(Pred,2), is_map(Map) ->
maps:from_list([{K,V}||{K,V}<-maps:to_list(Map),Pred(K,V)]);
filter(Pred,Map) ->
erlang:error(error_type(Map),[Pred,Map]).
1
Eiji
@cmkarlsson Ah … then it’s basically as same as Enum.filter/2 and Enum.into/2, but just in one function.
0
peerreynders
There really is no iteration functionality in Map - probably because that is represented in Enum.
iex(1)> data = %{
...(1)> requireInteraction: true,
...(1)> title: "title",
...(1)> body: "body",
...(1)> icon: nil,
...(1)> click_action: :click_action
...(1)> }
%{
body: "body",
click_action: :click_action,
icon: nil,
requireInteraction: true,
title: "title"
}
iex(2)> new_data = data |> Enum.reject(fn {_key, value} -> is_nil(value) end) |> Map.new()
%{
body: "body",
click_action: :click_action,
requireInteraction: true,
title: "title"
}
iex(3)> other_data = for kv <- data, (fn {_k,v} -> not is_nil(v) end).(kv), into: %{}, do: kv
%{
body: "body",
click_action: :click_action,
requireInteraction: true,
title: "title"
}
iex(4)>
Whichever way you look at it, it is filtered as a list.
1
gregvaughn
I’ve written a helper function for this sort of thing before
def maybe_put(map, _key, nil), do: map
def maybe_put(map, key, value), do: Map.put(map, key, value)
Then you can use for multiple fields and pipe easily, for example:
data = %{
requireInteraction: true,
title: title,
icon: icon,
click_action: click_action
}
|> maybe_put(:body, body)
|> maybe_put(:other_field, other_value)
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