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February 17, 2024 18:28
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Rust `group_by` (Reader discretion is advised)
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| use core::cell::RefCell; | |
| use std::collections::{BTreeMap, VecDeque}; | |
| use std::rc::Rc; | |
| pub trait GroupBy<Item> { | |
| fn group(self) -> impl Iterator<Item = (Item, impl Iterator<Item = Item>)> | |
| where | |
| Item: PartialEq + Copy; | |
| fn group_by<Key, KeyFn>( | |
| self, | |
| key: KeyFn, | |
| ) -> impl Iterator<Item = (Key, impl Iterator<Item = Item>)> | |
| where | |
| Key: PartialEq + Copy, | |
| KeyFn: Fn(&Item) -> Key; | |
| } | |
| impl<Iter, Item> GroupBy<Item> for Iter | |
| where | |
| Iter: Iterator<Item = Item>, | |
| { | |
| fn group(self) -> impl Iterator<Item = (Item, impl Iterator<Item = Item>)> | |
| where | |
| Item: PartialEq + Copy, | |
| { | |
| Groups { | |
| internal: Rc::new(RefCell::new(GroupsInternal { | |
| iter: self, | |
| key: |item| *item, | |
| buffers: BTreeMap::new(), | |
| current_id: 0, | |
| current_key: None, | |
| pending: false, | |
| })), | |
| } | |
| } | |
| fn group_by<Key, KeyFn>( | |
| self, | |
| key: KeyFn, | |
| ) -> impl Iterator<Item = (Key, impl Iterator<Item = Item>)> | |
| where | |
| Key: PartialEq + Copy, | |
| KeyFn: Fn(&Item) -> Key, | |
| { | |
| Groups { | |
| internal: Rc::new(RefCell::new(GroupsInternal { | |
| iter: self, | |
| key: key, | |
| buffers: BTreeMap::new(), | |
| current_id: 0, | |
| current_key: None, | |
| pending: false, | |
| })), | |
| } | |
| } | |
| } | |
| struct GroupsInternal<Iter, Item, Key, KeyFn> | |
| where | |
| Iter: Iterator<Item = Item>, | |
| Key: PartialEq + Copy, | |
| KeyFn: Fn(&Item) -> Key, | |
| { | |
| iter: Iter, | |
| key: KeyFn, | |
| buffers: BTreeMap<u64, VecDeque<Item>>, | |
| current_id: u64, | |
| current_key: Option<Key>, | |
| pending: bool, | |
| } | |
| struct Groups<Iter, Item, Key, KeyFn> | |
| where | |
| Iter: Iterator<Item = Item>, | |
| Key: PartialEq + Copy, | |
| KeyFn: Fn(&Item) -> Key, | |
| { | |
| internal: Rc<RefCell<GroupsInternal<Iter, Item, Key, KeyFn>>>, | |
| } | |
| impl<Iter, Item, Key, KeyFn> Iterator for Groups<Iter, Item, Key, KeyFn> | |
| where | |
| Iter: Iterator<Item = Item>, | |
| Key: PartialEq + Copy, | |
| KeyFn: Fn(&Item) -> Key, | |
| { | |
| type Item = (Key, Group<Iter, Item, Key, KeyFn>); | |
| fn next(&mut self) -> Option<Self::Item> { | |
| let mut internal = self.internal.borrow_mut(); | |
| let current_id = internal.current_id; | |
| if internal.pending { | |
| internal.pending = false; | |
| return Some(( | |
| internal.current_key.unwrap(), | |
| Group { | |
| internal: self.internal.clone(), | |
| id: current_id, | |
| }, | |
| )); | |
| } | |
| loop { | |
| if let Some(next) = internal.iter.next() { | |
| let key = (internal.key)(&next); | |
| if let Some(current_key) = internal.current_key { | |
| if key == current_key { | |
| if let Some(buffer) = internal.buffers.get_mut(¤t_id) { | |
| buffer.push_back(next); | |
| } | |
| } else { | |
| let next_id = current_id + 1; | |
| internal.buffers.insert(next_id, VecDeque::from([next])); | |
| internal.current_id = next_id; | |
| internal.current_key = Some(key); | |
| return Some(( | |
| key, | |
| Group { | |
| internal: self.internal.clone(), | |
| id: next_id, | |
| }, | |
| )); | |
| } | |
| } else { | |
| internal.buffers.insert(current_id, VecDeque::from([next])); | |
| internal.current_key = Some(key); | |
| return Some(( | |
| key, | |
| Group { | |
| internal: self.internal.clone(), | |
| id: current_id, | |
| }, | |
| )); | |
| } | |
| } else { | |
| return None; | |
| } | |
| } | |
| } | |
| } | |
| struct Group<Iter, Item, Key, KeyFn> | |
| where | |
| Iter: Iterator<Item = Item>, | |
| Key: PartialEq + Copy, | |
| KeyFn: Fn(&Item) -> Key, | |
| { | |
| internal: Rc<RefCell<GroupsInternal<Iter, Item, Key, KeyFn>>>, | |
| id: u64, | |
| } | |
| impl<Iter, Item, Key, KeyFn> Iterator for Group<Iter, Item, Key, KeyFn> | |
| where | |
| Iter: Iterator<Item = Item>, | |
| Key: PartialEq + Copy, | |
| KeyFn: Fn(&Item) -> Key, | |
| { | |
| type Item = Item; | |
| fn next(&mut self) -> Option<Self::Item> { | |
| let mut internal = self.internal.borrow_mut(); | |
| if let Some(next) = internal.buffers.get_mut(&self.id).unwrap().pop_front() { | |
| return Some(next); | |
| } | |
| if internal.current_id == self.id { | |
| if let Some(next) = internal.iter.next() { | |
| let key = (internal.key)(&next); | |
| if key == internal.current_key.unwrap() { | |
| return Some(next); | |
| } else { | |
| let next_id = internal.current_id + 1; | |
| internal.buffers.insert(next_id, VecDeque::from([next])); | |
| internal.current_id = next_id; | |
| internal.current_key = Some(key); | |
| internal.pending = true; | |
| } | |
| } | |
| } | |
| None | |
| } | |
| } | |
| impl<Iter, Item, Key, KeyFn> Drop for Group<Iter, Item, Key, KeyFn> | |
| where | |
| Iter: Iterator<Item = Item>, | |
| Key: PartialEq + Copy, | |
| KeyFn: Fn(&Item) -> Key, | |
| { | |
| fn drop(&mut self) { | |
| self.internal.borrow_mut().buffers.remove(&self.id); | |
| } | |
| } |
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