can someone please explain to me how Enum.reduce works with maps

Using Enum.reduce ultimately delegates to the protocol function Enumerable.reduce, which is implemented for Map here: https://github.com/elixir-lang/elixir/blob/79388035f5391f0a283a48fba792ae3b4f4b5f21/lib/elixir/lib/enum.ex#L3351-L3353 This first converts the Map to a list of {key, value} tuples,…

alphabet_positions = {"a" => 1, "b" => 2, "c" => 3, ...} Enum.reduce(alphabet_positions, 0, fn({letter, number}, accumulator) -> if "aeiou" =~ letter do accumulator += number end accumulator end) This trivial example adds up the positions of all the vowels in the alphabet.

Maps implement the Enumerable protocol. That implementation turns the map into a list of key-value tuples - see Map.to_list/1 (the actual implementation uses the Erlang version ). What is being reduced is the resulting list of key-value tuples, not the map itself - which goes something like this: i…

That won’t work, there is no += in elixir. I think what you really mean is more like this: alphabet_positions = %{"a" => 1, "b" => 2, "c" => 3, …} Enum.reduce(alphabet_positions, 0, fn {letter, position}, sum -> if letter in ~w[a e i o u], do: sum + position, else: sum end)

[image] peerreynders: That implementation turns the map into a keyword list No, its turned into a list of tuples with the key as the first element and the corresponding values as the second. The implementation of Map.to_list/1 is equivalent to this: map |> Map.keys() |> Enum.reduce([], fn ke…

[image] NobbZ: is equivalent to this Looks like it uses an internal iterator to avoid redundant traversals: https://github.com/erlang/otp/blob/master/lib/stdlib/src/maps.erl#L116-L127

Have tried this and the result is true which can also be implented this way: Enum.reduce(%{“a” => 1, “b” => 2}, , fn {k, v}, acc → [{k, v} | acc] end) [{“b”, 2}, {“a”, 1}]

your example returns the accumalator of the last vowel which i understand it will be the initial position of the last vowel added to accumulator giving you 6

Going the other way (list to map) Map.new/2 can be helpful. iex(1)> square_tuple = fn x -> {x , x * x} end #Function<7.91303403/1 in :erl_eval.expr/5> iex(2)> result = Map.new(1..10, square_tuple) %{ 1 => 1, 2 => 4, 3 => 9, 4 => 16, 5 => 25, 6 => 36, 7 => 49, 8 => 64, 9 => 81, 1…

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Enumerables - how does Enum.reduce work with maps

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Tee September 22, 2019, 1:31pm 3

it would be nice with an example that i can relate with