rms.mrcs
Transform a list into an map with indexes using Enum module
Hi,
I need to transform a list of numbers into a map where the keys are the indexes and the values are the original values of the list. I’ve managed to do this using the following code:
def indexed_map(list, index \\ 1, step \\ 1) do
to_indexed_map(list, index,step, %{})
end
defp to_indexed_map([h|t], i, s, acc),do: to_indexed_map(t, i + s, s, Map.put(acc, i, h))
defp to_indexed_map([], _, _, acc), do: acc
Basically if I apply this function to
[100, 200, 300]
it will return
%{1 => 100, 2 => 200, 3 => 300}
Is there any way to the same using Elixir’s standard library? I tried Enum.map, Enum.reduce and even Enum.map_reduce but I just couldn’t figure out how to it using them.
Thanks
Marked As Solved
Linuus
Something like this should work:
list = [100, 200, 300]
Stream.with_index(list, 1) |> Enum.reduce(%{}, fn({v,k}, acc)-> Map.put(acc, k, v) end)
Or this 
1..length(list) |> Stream.zip(list) |> Enum.into(%{})
Also Liked
andre1sk
There is prob a better way then this:
list |> Enum.with_index(1) |>Enum.map(fn {k,v}->{v,k} end) |> Map.new
OvermindDL1
Or shorter (by actually creating the tuple in-order instead of needing to swap it and not getting the length of a list, which can be O(n) instead of O(1)):
iex> list = [:a,:b,:c,:d,:e]
iex> Stream.zip(Stream.iterate(0, &(&1+1)), list) |> Enum.into(%{})
%{0 => :a, 1 => :b, 2 => :c, 3 => :d, 4 => :e}
An aside, I wish 0.. was a shortcut for (Stream.iterate(0, &(&1+1)), or maybe 0...1 means (Stream.iterate(0, &(&1+1)) like 0...-4 means (Stream.iterate(0, &(&1-4)) or so, ah well I wish, but it does not for now. Hmm, lot of ideas popping into mind for such a syntax, we need a Stream.seq/1.
Popular in Questions
Other popular topics
Latest on Elixir Forum
Sponsor Spotlight
We build reliable cloud platforms for business-critical systems.
Categories:
Sub Categories:
Forums
Popular Tags
- #ecto
- #liveview
- #troubleshooting
- #learning-elixir
- #deployment
- #library
- #erlang
- #testing
- #genserver
- #mix
- #absinthe
- #remote-other
- #otp
- #plug
- #how-to-question
- #macros
- #postgres
- #channels
- #elixirconf
- #exunit
- #discussion
- #code-sync
- #javascript
- #podcasts
- #onsite
- #dialyzer
- #docker
- #authentication
- #umbrella
- #full-time-contract
- #podcasts-by-brainlid
- #ecto-query
- #elixir-ls
- #phoenix_html
- #iex
- #blog-post
- #graphql
- #genstage
- #ai
- #websockets
- #supervisor
- #advent-of-code
- #elixirconf-us
- #distillery
- #processes
- #forms
- #api
- #metaprogramming
- #security
- #performance
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Catch errors, track performance, monitor hosts and more.
Real-time error tracking, performance insights, and observability for devs.
Practical resources that improve the lives of professional developers.
Enabling companies to succeed by building software people love.
The deployment platform built for Elixir: PaaS ease, VPS control.
Courses that'll move you from confusion to "Aha, now I get it!"