Sparse Table Implementation (Row, Col) -> Val

util/src/lib.rs

@@ -144,6 +144,7 @@ pub mod network;
 pub mod log;
 pub mod panics;
 pub mod keys;
+pub mod table;
 
 pub use common::*;
 pub use misc::*;

util/src/table.rs

@@ -0,0 +1,260 @@
+// Copyright 2015, 2016 Ethcore (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+//! A collection associating pair of keys (row and column) with a single value.
+
+use std::hash::Hash;
+use std::collections::HashMap;
+
+/// Structure to hold double-indexed values
+///
+/// You can obviously use `HashMap<(Row,Col), Val>`, but this structure gives
+/// you better access to all `Columns` in Specific `Row`. Namely you can get sub-hashmap
+/// `HashMap<Col, Val>` for specific `Row`
+pub struct Table<Row, Col, Val>
+	where Row: Eq + Hash + Clone,
+		  Col: Eq + Hash {
+	map: HashMap<Row, HashMap<Col, Val>>,
+}
+
+impl<Row, Col, Val> Table<Row, Col, Val>
+	where Row: Eq + Hash + Clone,
+		  Col: Eq + Hash {
+	/// Creates new Table
+	pub fn new() -> Table<Row, Col, Val> {
+		Table {
+			map: HashMap::new(),
+		}
+	}
+
+	/// Removes all elements from this Table
+	pub fn clear(&mut self) {
+		self.map.clear();
+	}
+
+	/// Returns length of the Table (number of (row, col, val) tuples)
+	pub fn len(&self) -> usize {
+		self.map.iter().fold(0, |acc, (_k, v)| acc + v.len())
+	}
+
+	/// Check if there is any element in this Table
+	pub fn is_empty(&self) -> bool {
+		self.len() == 0
+	}
+
+	/// Get mutable reference for single Table row.
+	pub fn get_row_mut(&mut self, row: &Row) -> Option<&mut HashMap<Col, Val>> {
+		self.map.get_mut(row)
+	}
+
+	/// Checks if row is defined for that table (note that even if defined it might be empty)
+	pub fn has_row(&self, row: &Row) -> bool {
+		self.map.contains_key(row)
+	}
+
+	/// Get immutable reference for single row in this Table
+	pub fn get_row(&self, row: &Row) -> Option<&HashMap<Col, Val>> {
+		self.map.get(row)
+	}
+
+	/// Get element in cell described by `(row, col)`
+	pub fn get(&self, row: &Row, col: &Col) -> Option<&Val> {
+		self.map.get(row).and_then(|r| r.get(col))
+	}
+
+	/// Remove value from specific cell
+	///
+	/// It will remove the row if it's the last value in it
+	pub fn remove(&mut self, row: &Row, col: &Col) -> Option<Val> {
+		let (val, is_empty) = {
+			let row_map = self.map.get_mut(row);
+			if let None = row_map {
+				return None;
+			}
+			let mut row_map = row_map.unwrap();
+			let val = row_map.remove(col);
+			(val, row_map.is_empty())
+		};
+		// Clean row
+		if is_empty {
+			self.map.remove(row);
+		}
+		val
+	}
+
+	/// Remove given row from Table if there are no values defined in it
+	///
+	/// When using `#get_row_mut` it may happen that all values from some row are drained.
+	/// Table however will not be aware that row is empty.
+	/// You can use this method to explicitly remove row entry from the Table.
+	pub fn clear_if_empty(&mut self, row: &Row) {
+		let is_empty = self.map.get(row).map_or(false, |m| m.is_empty());
+		if is_empty {
+			self.map.remove(row);
+		}
+	}
+
+	/// Inserts new value to specified cell
+	///
+	/// Returns previous value (if any)
+	pub fn insert(&mut self, row: Row, col: Col, val: Val) -> Option<Val> {
+		if !self.map.contains_key(&row) {
+			let m = HashMap::new();
+			self.map.insert(row.clone(), m);
+		}
+
+		let mut columns = self.map.get_mut(&row).unwrap();
+		columns.insert(col, val)
+	}
+}
+
+#[cfg(test)]
+mod test {
+	use super::*;
+
+	#[test]
+	fn should_create_empty_table() {
+		// when
+		let table : Table<usize, usize, bool> = Table::new();
+
+		// then
+		assert!(table.is_empty());
+		assert_eq!(table.len(), 0);
+	}
+
+	#[test]
+	fn should_insert_elements_and_return_previous_if_any() {
+		// given
+		let mut table = Table::new();
+
+		// when
+		let r1 = table.insert(5, 4, true);
+		let r2 = table.insert(10, 4, true);
+		let r3 = table.insert(10, 10, true);
+		let r4 = table.insert(10, 10, false);
+
+		// then
+		assert!(r1.is_none());
+		assert!(r2.is_none());
+		assert!(r3.is_none());
+		assert!(r4.is_some());
+		assert!(!table.is_empty());
+		assert_eq!(r4.unwrap(), true);
+		assert_eq!(table.len(), 3);
+	}
+
+	#[test]
+	fn should_remove_element() {
+		// given
+		let mut table = Table::new();
+		table.insert(5, 4, true);
+		assert!(!table.is_empty());
+		assert_eq!(table.len(), 1);
+
+		// when
+		let r = table.remove(&5, &4);
+
+		// then
+		assert!(table.is_empty());
+		assert_eq!(table.len() ,0);
+		assert_eq!(r.unwrap(), true);
+	}
+
+	#[test]
+	fn should_return_none_if_trying_to_remove_non_existing_element() {
+				// given
+		let mut table : Table<usize, usize, usize> = Table::new();
+		assert!(table.is_empty());
+
+		// when
+		let r = table.remove(&5, &4);
+
+		// then
+		assert!(r.is_none());
+	}
+
+	#[test]
+	fn should_clear_row_if_removing_last_element() {
+		// given
+		let mut table = Table::new();
+		table.insert(5, 4, true);
+		assert!(table.has_row(&5));
+
+		// when
+		let r = table.remove(&5, &4);
+
+		// then
+		assert!(r.is_some());
+		assert!(!table.has_row(&5));
+	}
+
+	#[test]
+	fn should_return_element_given_row_and_col() {
+		// given
+		let mut table = Table::new();
+		table.insert(1551, 1234, 123);
+
+		// when
+		let r1 = table.get(&1551, &1234);
+		let r2 = table.get(&5, &4);
+
+		// then
+		assert!(r1.is_some());
+		assert!(r2.is_none());
+		assert_eq!(r1.unwrap(), &123);
+	}
+
+	#[test]
+	fn should_clear_table() {
+		// given
+		let mut table = Table::new();
+		table.insert(1, 1, true);
+		table.insert(1, 2, false);
+		table.insert(2, 2, false);
+		assert_eq!(table.len(), 3);
+
+		// when
+		table.clear();
+
+		// then
+		assert!(table.is_empty());
+		assert_eq!(table.len(), 0);
+		assert_eq!(table.has_row(&1), false);
+		assert_eq!(table.has_row(&2), false);
+	}
+
+	#[test]
+	fn should_return_mutable_row() {
+		// given
+		let mut table = Table::new();
+		table.insert(1, 1, true);
+		table.insert(1, 2, false);
+		table.insert(2, 2, false);
+
+		// when
+		{
+			let mut row = table.get_row_mut(&1).unwrap();
+			row.remove(&1);
+			row.remove(&2);
+		}
+		assert!(table.has_row(&1));
+		table.clear_if_empty(&1);
+
+		// then
+		assert!(!table.has_row(&1));
+		assert_eq!(table.len(), 1);
+	}
+}