l1 = ["1","2","5","9"] l2 = ["1","9"] List.contains?(l1,l2) Anything like this? to check if l2 is a sublist of l1. I know can use Enum.each and check one by one, just want to know if anything like that. thanks

l2 is not a sublist of l1. But in general, sublist checking is quite easy to do. def sublist?([], _), do: false def sublist?(l1 = [_|t], l2) do List.starts_with?(l1, l2) or sublist?(t, l2) end

def subset(_, []), do: true def subset([], _), do: false def subset([h | t1], [h | t2]), do: subset(t1, t2) def subset([_ | t], list), do: subset(t, list)

[image] Ajaxdone: l1 = ["1","2","5","9"] l2 = ["1","9"] Maybe I need to clarify a bit, actually I don’t mean sublist, I mean a list’s all items in another list, don’t care order.

Then mapset might indeed be the most efficient way to do so.

I tested your solutions, in my previous dataset is works, but if change to this, not working: l1 = ["9","2","5","1"] l2 = ["1","9"]

Yes, @hauleths approach is for pre-ordered input only.

According to @NobbZ 's suggestion as well, I tried this one works: big_list = ["9", "2", "5", "1"] sub_out_of_order_list = ["1", "9"] MapSet.subset?(MapSet.new(sub_out_of_order_list), MapSet.new(big_list)) Thank you everyone.

Depending on the relative sizes of your lists, this could also be a viable option: Enum.all?(sub_out_of_order_list, &Enum.member?(big_list, &1))

I am only using to check roles, so relative small lists for both. If really want to check in very large list, then better sort the sub one first, and then search in :orddict or Map. But no matter what I think MapSet still very fast on large list, as when convert to Set, using hashcode to search sh…

Giving this 2 lists: [1, 3], [1, 2, 3] In this case, MapSet.subset? returns true, but [1,3] is not a subset of [1,2,3]… iex(1)> MapSet.subset?(MapSet.new([1, 3]), MapSet.new([1, 2, 3])) true

Elixir Programming Language Forum

How to check if a list is a sublist(out of order list) of another list

Questions & Help Questions

emoragaf July 7, 2020, 8:32pm 2

maybe using MapSet.subset?/2