[optimize] Context -- use double index entityAttributeIndex and `…

…attributeEntityIndex`

TODO.md

@@ -1,10 +1,15 @@
+# lattice layout
+
 练习 order book 中计算 concept lattice 的算法。
 
-- 也许可以以这个算法为基础，来给出 lattice 的 layout。
+- 以这个算法为基础，来给出 lattice 的 layout。
 
-`concept-graph/` -- 从 `generateConcepts` 生成有向图
+`concept-graph/` -- 以 `generateConcepts` 的结果为基础，生成有向图
 
-- 以 concept 之间的蕴含关系为 有向边
+- 以 concept 之间的蕴含关系为有向边 -- 方向就是蕴含关系的方向
+- 可能的 API：
+  - `LatticeLayout`
+  - `layoutLattice(context)`
 
 找出 lattice 中的所有最长 chain -- 为计算 rank 做准备
 
@@ -15,15 +20,6 @@
 - 注意，我们要对所有点找到最长的 chain，
   最好能一起找，而不只是一个点一个点的找。
 
-# lattice layout
-
-`LatticeLayout`
-`layoutLattice(context)`
-
-# optimize
-
-`Context` -- use double index `entityAttributeIndex` and `attributeEntityIndex`
-
 # editing context
 
 如何处理对 context 的修改？

src/context/Context.ts

@@ -4,5 +4,6 @@ export type Attribute = string
 export type Context = Readonly<{
   entities: ReadonlySet<Entity>
   attributes: ReadonlySet<Attribute>
-  entityAttributeIndex: ReadonlyMap<string, ReadonlySet<string>>
+  entityAttributeIndex: ReadonlyMap<Entity, ReadonlySet<Attribute>>
+  attributeEntityIndex: ReadonlyMap<Attribute, ReadonlySet<Entity>>
 }>

src/context/attributesOf.ts

@@ -4,10 +4,5 @@ export function attributesOf(
   context: Context,
   entity: Entity,
 ): ReadonlySet<Attribute> {
-  const attributes = context.entityAttributeIndex.get(entity)
-  if (attributes === undefined) {
-    return new Set()
-  }
-
-  return attributes
+  return context.entityAttributeIndex.get(entity) || new Set()
 }

src/context/createContextFromCrossTable.ts

@@ -6,13 +6,24 @@ export function createContextFromCrossTable(table: CrossTable): Context {
     entities: new Set<Entity>(),
     attributes: new Set<Attribute>(),
     entityAttributeIndex: new Map<Entity, Set<Attribute>>(),
+    attributeEntityIndex: new Map<Attribute, Set<Entity>>(),
   }
 
   context.entities = new Set(Object.keys(table))
   context.attributes = new Set(Object.values(table).flat())
+
   for (const [entity, attributes] of Object.entries(table)) {
     context.entityAttributeIndex.set(entity, new Set(attributes))
   }
 
+  for (const [entity, attributes] of Object.entries(table)) {
+    for (const attribute of attributes) {
+      let entities = context.attributeEntityIndex.get(attribute)
+      if (entities === undefined) entities = new Set()
+      context.attributeEntityIndex.set(attribute, entities)
+      entities.add(entity)
+    }
+  }
+
   return Object.freeze(context)
 }

src/context/entitiesOf.ts

@@ -1,16 +1,8 @@
 import type { Attribute, Context, Entity } from "./Context.js"
-import { attributesOf } from "./attributesOf.js"
 
 export function entitiesOf(
   context: Context,
   attribute: Attribute,
 ): ReadonlySet<Entity> {
-  const entities = new Set<Entity>()
-  for (const entity of context.entities) {
-    if (attributesOf(context, entity).has(attribute)) {
-      entities.add(entity)
-    }
-  }
-
-  return entities
+  return context.attributeEntityIndex.get(attribute) || new Set()
 }