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sorted_set.ex
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sorted_set.ex
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defmodule Dasie.SortedSet do
@moduledoc """
A sorted set is a non-repeating collection of keys. Every key
is also associated with a score. While keys are unique, scores may be repeated.
This way you can get a range of keys based on their score in an efficient way.
Like the Redis implementation
we keep two "views" of the data at all times. One optimized for
key access (using a hash map), and one for scores (using a red black tree).
Reference:
- https://redis.io/topics/data-types#sorted-sets
- https://github.com/antirez/redis/blob/unstable/src/t_zset.c
"""
alias Dasie.RedBlackTree
defstruct scores: nil,
keys: nil
@type t :: %__MODULE__{
scores: Dasie.RedBlackTree.t() | nil,
keys: map | nil
}
@doc "Create a new empty sorted set"
@spec new() :: __MODULE__.t()
def new(), do: %__MODULE__{scores: RedBlackTree.new(), keys: %{}}
@doc "Create a new sorted set with key and score."
@spec new(key :: any, score :: integer) :: __MODULE__.t()
def new(key, score) do
%__MODULE__{
scores: RedBlackTree.new({score, key}),
keys: %{key => score}
}
end
@doc "Create a new sorted set with a list of `{keys, score}`"
@spec new(list({any, integer})) :: __MODULE__.t()
def new([first | rest]) do
{key1, score1} = first
keys =
Enum.reduce(rest, %{key1 => score1}, fn {key, score}, acc ->
Map.put(acc, key, score)
end)
scores =
Enum.reduce(rest, RedBlackTree.new({score1, key1}), fn {key, score}, acc ->
if Map.get(keys, key) == score do
RedBlackTree.insert(acc, {score, key})
else
acc
end
end)
%__MODULE__{keys: keys, scores: scores}
end
@doc "Insert a new key, score into the sorted set"
@spec insert(set :: __MODULE__.t(), key :: any, score :: integer) :: __MODULE__.t()
def insert(%__MODULE__{} = set, key, score) do
existing_score = Map.get(set.keys, key)
scores =
if existing_score == nil do
RedBlackTree.insert(set.scores, {score, key})
else
update(set.scores, {existing_score, key}, {score, key})
end
%__MODULE__{keys: Map.put(set.keys, key, score), scores: scores}
end
@doc "Insert a list of {key, score} tuples into the sorted set"
@spec insert(set :: __MODULE__.t(), list({any, integer}) | {any, integer}) :: __MODULE__.t()
def insert(%__MODULE__{} = set, elements) when is_list(elements) do
keys =
Enum.reduce(elements, set.keys, fn {key, score}, acc ->
Map.put(acc, key, score)
end)
scores =
Enum.reduce(elements, set.scores, fn element, acc ->
insertion(set.keys, keys, element, acc)
end)
%__MODULE__{keys: keys, scores: scores}
end
def insert(%__MODULE__{} = set, {key, score}) do
insert(set, key, score)
end
defp insertion(old_keys, new_keys, {key, score}, acc) do
existing_score = Map.get(old_keys, key)
new_score = Map.get(new_keys, key)
cond do
score != new_score ->
acc
existing_score == nil ->
RedBlackTree.insert(acc, {score, key})
existing_score == score ->
acc
true ->
update(acc, {existing_score, key}, {score, key})
end
end
defp update(%RedBlackTree{} = scores, existing, updated) do
deleted = RedBlackTree.delete(scores, existing)
if deleted == nil do
RedBlackTree.new(updated)
else
RedBlackTree.insert(deleted, updated)
end
end
@doc "Return a list of keys and their scores in the set"
@spec to_list(set :: __MODULE__.t()) :: list({any, integer})
def to_list(%__MODULE__{keys: keys}) do
keys
|> Map.to_list()
|> Enum.sort()
end
@doc "Returns a list of keys, with scores that are within the range (inclusive)"
def range(%__MODULE__{scores: scores}, first..last) do
range(scores, first, last, [])
|> Enum.sort()
|> Enum.map(&external_format/1)
end
@spec range(set :: __MODULE__.t() | nil, first :: integer, last :: integer, acc :: list) :: list({any, integer})
def range(nil, _, _, acc), do: acc
def range(
%RedBlackTree{data: {score, _key} = element, left: nil, right: nil},
first,
last,
acc
)
when score >= first and score <= last do
[element | acc]
end
def range(%RedBlackTree{data: {score, _key} = element, left: nil} = rbt, first, last, acc)
when score >= first and score <= last do
[element | range(rbt.right, first, last, acc)]
end
def range(%RedBlackTree{data: {score, _key} = element, right: nil} = rbt, first, last, acc)
when score >= first and score <= last do
[element | range(rbt.left, first, last, acc)]
end
def range(%RedBlackTree{data: {score, _key} = element} = rbt, first, last, acc)
when score >= first and score <= last do
[element] ++ range(rbt.left, first, last, acc) ++ range(rbt.right, first, last, acc)
end
def range(%RedBlackTree{left: nil} = rbt, first, last, acc) do
range(rbt.right, first, last, acc)
end
def range(%RedBlackTree{right: nil} = rbt, first, last, acc) do
range(rbt.left, first, last, acc)
end
def range(%RedBlackTree{} = rbt, first, last, acc) do
range(rbt.left, first, last, acc) ++ range(rbt.right, first, last, acc)
end
@doc "Deletes a key from the set"
@spec delete(set :: __MODULE__.t(), key :: any) :: __MODULE__.t()
def delete(%__MODULE__{} = set, key) do
existing_score = Map.get(set.keys, key)
if existing_score == nil do
set
else
%__MODULE__{
keys: Map.delete(set.keys, key),
scores: RedBlackTree.delete(set.scores, {existing_score, key})
}
end
end
@doc "Checks if key exists in the set"
@spec member?(set :: __MODULE__.t(), key :: any) :: boolean
def member?(%__MODULE__{} = set, key) do
Map.has_key?(set.keys, key)
end
defp external_format({score, key}), do: {key, score}
defimpl Collectable, for: Dasie.SortedSet do
def into(original) do
collector_fun = fn
set, {:cont, elem} -> Dasie.SortedSet.insert(set, elem)
set, :done -> set
_set, :halt -> :ok
end
{original, collector_fun}
end
end
end