RazgrizHsu
we can create a list like this
list = [ a: 1, b: 2, c: 3 ]
but i can’t found api to add element with key to list?
list = []
key = :a
value = 1
#wrong ( * (SyntaxError) iex:4: syntax error before: '=>' )
list = list ++ [ key => value ]
anyone know how to do that?
thank you 
Where Next?
Trending in Questions
Other Trending Topics
Latest on Elixir Forum
Sponsor Spotlight
Build Elixir applications with speed and confidence.
Categories:
Sub Categories:
Forums
Popular Tags
- #ecto
- #liveview
- #troubleshooting
- #learning-elixir
- #library
- #deployment
- #erlang
- #testing
- #genserver
- #mix
- #absinthe
- #remote-other
- #otp
- #plug
- #how-to-question
- #macros
- #postgres
- #elixirconf
- #channels
- #exunit
- #discussion
- #code-sync
- #podcasts
- #javascript
- #onsite
- #dialyzer
- #docker
- #authentication
- #umbrella
- #full-time-contract
- #podcasts-by-brainlid
- #ecto-query
- #blog-post
- #elixirconf-us
- #elixir-ls
- #ai
- #phoenix_html
- #iex
- #graphql
- #genstage
- #websockets
- #supervisor
- #advent-of-code
- #distillery
- #processes
- #api
- #forms
- #hex
- #security
- #metaprogramming
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Error tracking, logs, uptime, and Just Enough APM. Built for developers.
Elixir, Erlang & BEAM conferences from Code Sync - join us in 2026!
Master modern tools, write cleaner code, and tackle real-world challenges.
Bringing learning, work and compliance together since 1987.
**Building the future of software with AI, trust, and human connection.**
The team behind Membrane, Popcorn, LiveDebugger. Available for hire.
Courses that'll move you from confusion to "Aha, now I get it!"
Showing Posts 1 to 6- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
LostKobrakai
Keyword lists are syntax sugar over a list of tuples, which are strictly
{atom(), term()}. So you can dolist ++ [{key, value}].lpil
As an extra tip,
list ++ [{key, value}]is quite slow as you need to traverse the entire list to add[{key, value}]to the end.As a rule of thumb you should add elements to the front of the list, which happens in constant time
[{key, value} | list]NobbZ
Besides from what have been said already, you also can use
Keyword.put/3.hauleth
Which is slower than
[{key, value} | list]as this need to traverse all list and remove duplicates.NobbZ
Yes, it is, but on the other hand side guarantees that the key is available only once and also that the kw list is a valid kw list.
Speed is not always everything.
RazgrizHsu
thank you very much guys, it’s great answer and performance advise