Hello! I’m trying to get more comfy with idiomatic elixir, and it seems like one line anonymous fn {} -> ... end calls might not be ideal. Maybe they are, but I’m curious if there’s a cleaner way to do a map over a map and get another map. Here’s what I have: Enum.map(m, fn {k,v}-> {k, length(v)} …

[image] mrkurt: Enum.map(m, fn {k,v}-> {k, length(v)} end) |> Map.new Actually Map.new/2 accepts a function, so you can also directly call Map.new(m, fn {k,v}-> {k, length(v)} end).

[image] mrkurt: Here’s what I have: Enum.map(m, fn {k,v}-> {k, length(v)} end) |> Map.new :maps.map(fn _k, v -> length(v) end, m) maybe not idiomatic, but erlang library comes in handy here.

I might use for: for {k, v} <- m, do: {k, length(v)}, into: %{}

What about skipping the first Enum.map? Map.new(m, & {elem(&1, 0), String.length(elem(&1, 1))}) [image] srowley: I might use for: for {k, v} <- m, do: {k, length(v)}, into: %{} You can also use for with reduce. for {k, v} <- m, reduce: %{} do acc -> Map.put(acc, k, String.length(v)) end o…

[image] mrkurt: Enum.map(m, fn {k,v}-> {k, length(v)} end) |> Map.new Sure! Enum.into(m, %{}, fn {k,v} -> {k,length(v)} end) Enum.into(%{a: [1], b: [1,2]}, %{}, fn {k,l} -> {k,length(l)} end)

It took 5 replies to get the most straight solution for such a simple question. :smiley: I believe normally people would write what mrkurt already wrote which is not “not concise” at all.

You might not have seen I used Map.new/2 in my reply :slight_smile:

Oh sorry I missed it! Also worth noting, Map.new/2 should be the fastest option as well according to this benchmark .

[image] sabiwara: Actually Map.new/2 accepts a function, so you can also directly call Map.new(m, fn {k,v}-> {k, length(v)} end). and [image] kokolegorille: What about skipping the first Enum.map? Map.new(m, & {elem(&1, 0), String.length(elem(&1, 1))}) Oh my gosh these are great. Tha…

Here’ s reply number 6. Enum.into(m, %{}, fn {k,v}-> {k, length(v)} end)

This would have been my solution, though I would have put the into: before the do:

Elixir Programming Language Forum

Map over a map and create a new map?

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kokolegorille February 23, 2021, 4:58am 8

You might not have seen I used Map.new/2 in my reply