anurag.peshne
what is the closest thing to Arrays in Elixir. By arrays I mean, a container for values which I can access in constant time.
I’ve looked at tuple, but according to the documentation:
Tuples are not meant to be used as a “collection” type (which is also suggested by the absence of an implementation of the Enumerable protocol for tuples): they’re mostly meant to be used as a fixed-size container for multiple elements.
What I actually want to do:
I want to store n processes in an array and periodically pick a random process and send it a message.
I’m open to other suggestions too.
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sjoconnor
You’re probably looking for
List. You could then do something like this to grab a random entry:[1,2,3] |> Enum.take_random(1)anurag.peshne
Unfortunately this will traverse list linearly. I’m looking for constant time lookup.
kokolegorille
You can use a map, and periodically pick a random key ?!
anurag.peshne
Yes, that’s the last resort. I just want to make sure I’m not missing any data structure.
kokolegorille
There is also Keyword, but the order of the key is not preserved over 32000 keys… and they act as List, so there is no constant time access.
For your use case, I would probably choose a map.
kylethebaker
Does order matter? Do you need to access items by key or just at random? Map has been mentioned, but there is also MapSet if you don’t need keys. Both implement the enumerable protocol, so to get a random value you can pass it to
Enum.random. What I’ve done in the past when I want constant time lookups by key and also maintain order is to create two structures: a map for the constant lookups, and a list of keys for the order.You may also consider looking into using a Registry if you want a container for processes, though for your use case it might be easier to just keep simple collection of pids.
benwilson512
You may want to elaborate on your use case. Various datastructures (including arrays) have various performance characteristics for different kinds of operations and without knowing what operations you have in mind, it’s hard to recommend the best approach.
Tuples have constant lookup time, but have to be copied wholesale for every change, which is generally undesirable.
benwilson512
This seems wrong. A keyword list is just a list, and lists preserve their order at all sizes.
kokolegorille
@benwilson512 Yes You are right, it’s map which doesn’t keep order over 32 keys…
I have been mixing up, both types and numbers
benwilson512
Ah yeah. For maps it’s best to treat them as if they have no order at all, the fact that they happen to preserve order under 32 keys is explicitly just an artifact of how the algorithm works and should never be relied upon.