You've got:

• http://erlang.org/doc/man/atomics.html and http://erlang.org/doc/man/counters.html for cheap, mutable uint64 arrays;

• The http://erlang.org/doc/man/array.html module for a functional persistent vector abstraction (similar to the one in Clojure);

• ETS ordered_set tables, for mutable AVL trees (for when you want to cheaply apply a sequence of random mutations to a collection of terms without building a lot of garbage);

• The process dictionary (https://www.erlang.org/course/advanced#dict), a mutable per-process hash-map data-structure, for when ETS ordered_set tables have too much inter-process copying overhead.

All that, plus Erlang lists (singly-linked lists) are really cheap the way Erlang does them. (Each Erlang actor-process gets its own heap that gets independently GCed; short-lived processes never experience even a single GC, so allocating linked-list nodes (by consing to the beginning of a list) is just a matter of incrementing the actor-process's heap's free pointer—about the same level of optimality you'd hope to get from pushing to the end of a vector.)

Thanks! Didn't know about some of those.

You're mostly right!

http://erlang.org/doc/man/array.html

There is List, which is similar (but not quite the same).

Other than that, you may want to give this a read: https://elixirforum.com/t/arrays/8850/13

tl;dr: the type of data structure that would satisfy your use case almost certainly exists in Elixir, but you need to look around a bit.