fix: Implement Weighted Distance Algorithm (#2255)

* doc: add comments to suggest
* dev: First pass at Levenshtein
* dev: Add an A* distance calculation function.
* dev: Implement weighted distance

cspell-dict.txt

@@ -2,14 +2,15 @@ alexiosc
 backreference
 bitjson
 cheatsheets
-Codecov
 codecov
+Codecov
 codeql
 COMPOUNDFLAG
 coverallsapp
 cspellcache
-DAWG
+Damerau
 Dawg
+DAWG
 deserializers
 exonum
 gimu

packages/cspell-trie-lib/src/lib/suggestions/distanceAStar.test.ts

@@ -0,0 +1,18 @@
+import { distanceAStar } from './distanceAStar';
+import { levenshteinDistance } from './levenshtein';
+
+describe('distanceAStar', () => {
+    test.each`
+        wordA        | wordB
+        ${''}        | ${''}
+        ${'apple'}   | ${'apple'}
+        ${'apple'}   | ${''}
+        ${'apple'}   | ${'apples'}
+        ${'apple'}   | ${'maple'}
+        ${'grapple'} | ${'maples'}
+    `('distanceAStar vs Levenshtein "$wordA" "$wordB"', ({ wordA, wordB }) => {
+        const expected = levenshteinDistance(wordA, wordB) * 100;
+        expect(distanceAStar(wordA, wordB)).toBe(expected);
+        expect(distanceAStar(wordB, wordA)).toBe(expected);
+    });
+});

packages/cspell-trie-lib/src/lib/suggestions/distanceAStar.ts

@@ -0,0 +1,75 @@
+import { PairingHeap } from '../utils/PairingHeap';
+
+/**
+ * Calculate the edit distance between two words using an A* algorithm.
+ *
+ * Using basic weights, this algorithm has the same results as the Damerau-Levenshtein algorithm.
+ */
+export function distanceAStar(a: string, b: string): number {
+    const aN = a.length;
+    const bN = b.length;
+    const cost = 100;
+
+    const candidates = new PairingHeap(compare);
+
+    candidates.add({ ai: 0, bi: 0, c: 0 });
+
+    function opSub(n: Node) {
+        const { ai, bi, c } = n;
+        if (ai < aN && bi < bN) {
+            const cc = a[ai] === b[bi] ? c : c + cost;
+            candidates.add({ ai: ai + 1, bi: bi + 1, c: cc });
+        }
+    }
+
+    function opIns(n: Node) {
+        const { ai, bi, c } = n;
+        if (bi < bN) {
+            candidates.add({ ai: ai, bi: bi + 1, c: c + cost });
+        }
+    }
+
+    function opDel(n: Node) {
+        const { ai, bi, c } = n;
+        if (ai < aN) {
+            candidates.add({ ai: ai + 1, bi: bi, c: c + cost });
+        }
+    }
+
+    function opSwap(n: Node) {
+        const { ai, bi, c } = n;
+        if (a[ai] === b[bi + 1] && a[ai + 1] === b[bi]) {
+            candidates.add({ ai: ai + 2, bi: bi + 2, c: c + cost });
+        }
+    }
+
+    let best: Node | undefined;
+    // const bc2 = 2 * bc;
+    while ((best = candidates.dequeue())) {
+        if (best.ai === aN && best.bi === bN) break;
+
+        opSwap(best);
+        opIns(best);
+        opDel(best);
+        opSub(best);
+    }
+
+    return best?.c ?? -1;
+}
+
+interface Pos {
+    /** the offset in string `a` */
+    ai: number;
+    /** the offset in string `b` */
+    bi: number;
+}
+
+interface Node extends Pos {
+    /** the current cost */
+    c: number;
+}
+
+function compare(a: Node, b: Node): number {
+    // Choose lowest cost or farthest Manhattan distance.
+    return a.c - b.c || b.ai + b.bi - a.ai - a.bi;
+}

packages/cspell-trie-lib/src/lib/suggestions/distanceAStarWeighted.test.ts

@@ -0,0 +1,42 @@
+import { distanceAStarWeighted } from './distanceAStarWeighted';
+import { levenshteinDistance } from './levenshtein';
+import { buildWeightedMapTrie } from './weightedMaps';
+
+describe('distanceAStar', () => {
+    test.each`
+        wordA        | wordB
+        ${''}        | ${''}
+        ${'apple'}   | ${'apple'}
+        ${'apple'}   | ${''}
+        ${'apple'}   | ${'apples'}
+        ${'apple'}   | ${'maple'}
+        ${'grapple'} | ${'maples'}
+    `('distanceAStar vs Levenshtein "$wordA" "$wordB"', ({ wordA, wordB }) => {
+        const expected = levenshteinDistance(wordA, wordB) * 100;
+        expect(distanceAStarWeighted(wordA, wordB, {})).toBe(expected);
+        expect(distanceAStarWeighted(wordB, wordA, {})).toBe(expected);
+    });
+
+    // cspell:ignore aeiou
+    test.each`
+        wordA         | wordB                                    | map                                          | expected
+        ${''}         | ${''}                                    | ${undefined}                                 | ${0}
+        ${'apple'}    | ${'apple'}                               | ${{ map: 'ae', insDel: 75 }}                 | ${0}
+        ${'apple'}    | ${''}                                    | ${{ map: 'ae', insDel: 75 }}                 | ${450}
+        ${'apple'}    | ${''}                                    | ${{ map: 'ae|(ap)', insDel: 75 }}            | ${350}
+        ${'apple'}    | ${''}                                    | ${{ map: '(ap)', insDel: 1 }}                | ${301}
+        ${'apple'}    | ${'apples'}                              | ${{ map: '(les)(le)', replace: 50 }}         | ${50}
+        ${'apple'}    | ${'maple'}                               | ${{ map: '(pp)p', replace: 50 }}             | ${150}
+        ${'grapple'}  | ${'maples'}                              | ${{ map: '(pp)p', replace: 50 }}             | ${350}
+        ${'bite'}     | ${'bate'}                                | ${{ map: 'aei', replace: 25 }}               | ${25}
+        ${'receive'}  | ${'recieve' /* cspell:ignore recieve */} | ${{ map: 'ei', swap: 25 }}                   | ${25}
+        ${'airplane'} | ${'aeroplane'}                           | ${{ map: '(ai)(ae)', replace: 25 }}          | ${125}
+        ${'airplane'} | ${'aeroplane'}                           | ${{ map: '(air)(aero)|aeiou', replace: 25 }} | ${25}
+        ${'airplane'} | ${'aeroplane'}                           | ${{ map: 'aeiou', replace: 25 }}             | ${125}
+        ${'plain'}    | ${'plane'}                               | ${{ map: '(ane)(ain)', replace: 100 }}       | ${100}
+    `('distanceAStar vs Levenshtein "$wordA" "$wordB" $map', ({ wordA, wordB, map, expected }) => {
+        const trie = map ? buildWeightedMapTrie([map]) : buildWeightedMapTrie([]);
+        expect(distanceAStarWeighted(wordA, wordB, trie)).toBe(expected);
+        expect(distanceAStarWeighted(wordB, wordA, trie)).toBe(expected);
+    });
+});

packages/cspell-trie-lib/src/lib/suggestions/distanceAStarWeighted.ts

@@ -0,0 +1,168 @@
+import { PairingHeap } from '../utils/PairingHeap';
+import { WeightedMapTrie, WeightedRepMapTrie } from './weightedMaps';
+
+/**
+ * Calculate the edit distance between two words using an A* algorithm.
+ *
+ * Using basic weights, this algorithm has the same results as the Damerau-Levenshtein algorithm.
+ */
+export function distanceAStarWeighted(a: string, b: string, map: WeightedMapTrie): number {
+    const aN = a.length;
+    const bN = b.length;
+    const cost = 100;
+
+    const candidates = new PairingHeap(compare);
+
+    candidates.add({ ai: 0, bi: 0, c: 0 });
+
+    function opSub(n: Node) {
+        const { ai, bi, c } = n;
+        if (ai < aN && bi < bN) {
+            const cc = a[ai] === b[bi] ? c : c + cost;
+            candidates.add({ ai: ai + 1, bi: bi + 1, c: cc });
+        }
+    }
+
+    function opIns(n: Node) {
+        const { ai, bi, c } = n;
+        if (bi < bN) {
+            candidates.add({ ai: ai, bi: bi + 1, c: c + cost });
+        }
+    }
+
+    function opDel(n: Node) {
+        const { ai, bi, c } = n;
+        if (ai < aN) {
+            candidates.add({ ai: ai + 1, bi: bi, c: c + cost });
+        }
+    }
+
+    function opSwap(n: Node) {
+        const { ai, bi, c } = n;
+        if (a[ai] === b[bi + 1] && a[ai + 1] === b[bi]) {
+            candidates.add({ ai: ai + 2, bi: bi + 2, c: c + cost });
+        }
+    }
+
+    function opMap(n: Node) {
+        const { ai, bi, c } = n;
+
+        function ins(ai: number, bi: number, m: WeightedMapTrie | undefined) {
+            if (bi >= bN || !m) return;
+            const n = m[b[bi]];
+            if (!n) return;
+            const cost = n.insDel;
+            ++bi;
+            if (cost !== undefined) {
+                candidates.add({ ai, bi, c: c + cost });
+            }
+            ins(ai, bi, n.t);
+        }
+
+        function del(ai: number, bi: number, m: WeightedMapTrie | undefined) {
+            if (ai >= aN || !m) return;
+            const n = m[a[ai]];
+            if (!n) return;
+            ++ai;
+            const cost = n.insDel;
+            if (cost !== undefined) {
+                candidates.add({ ai, bi, c: c + cost });
+            }
+            del(ai, bi, n.t);
+        }
+
+        function repApply(ai: number, bi: number, m: WeightedRepMapTrie | undefined) {
+            if (!m || bi >= bN) return;
+            const char = b[bi];
+            const n = m[char];
+            if (!n) return;
+            ++bi;
+            const cost = n.rep;
+            if (cost !== undefined) {
+                candidates.add({ ai, bi, c: c + cost });
+            }
+            repApply(ai, bi, n.r);
+        }
+
+        function rep(ai: number, bi: number, m: WeightedMapTrie | undefined) {
+            if (!m || ai >= aN || bi >= bN) return;
+            const n = m[a[ai]];
+            if (!n) return;
+            ++ai;
+            repApply(ai, bi, n.r);
+            rep(ai, bi, n.t);
+        }
+
+        function swap(ai: number, bi: number, m: WeightedMapTrie | undefined) {
+            if (!m || ai >= aN || bi >= bN) return;
+
+            function apply(mid: number, right: number, cost: number | undefined) {
+                if (cost === undefined) return;
+                const swap = a.slice(mid, right) + a.slice(ai, mid);
+                const len = swap.length;
+
+                const subB = b.slice(bi, bi + len);
+                if (swap === subB) {
+                    candidates.add({ ai: ai + len, bi: bi + len, c: cost });
+                }
+            }
+
+            function right(aim: number, ail: number, m: WeightedRepMapTrie | undefined) {
+                if (!m || ail >= aN) return;
+                const n = m[a[ail]];
+                if (!n) return;
+                ++ail;
+                apply(aim, ail, n.swap);
+                right(aim, ail, n.r);
+            }
+
+            function left(aim: number, m: WeightedMapTrie | undefined) {
+                if (!m || aim >= aN) return;
+                const n = m[a[aim]];
+                if (!n) return;
+                ++aim;
+                right(aim, aim, n.r);
+                left(aim, n.t);
+            }
+
+            left(ai, m);
+        }
+
+        ins(ai, bi, map);
+        del(ai, bi, map);
+        rep(ai, bi, map);
+        swap(ai, bi, map);
+    }
+
+    let best: Node | undefined;
+    // const bc2 = 2 * bc;
+    while ((best = candidates.dequeue())) {
+        if (best.ai === aN && best.bi === bN) break;
+
+        opSwap(best);
+        opIns(best);
+        opDel(best);
+        opMap(best);
+        opSub(best);
+    }
+
+    // istanbul ignore else
+    return best ? best.c : -1;
+}
+
+interface Pos {
+    /** the offset in string `a` */
+    ai: number;
+    /** the offset in string `b` */
+    bi: number;
+}
+
+interface Node extends Pos {
+    /** the current cost */
+    c: number;
+}
+
+function compare(a: Node, b: Node): number {
+    // Choose lowest cost or farthest Manhattan distance.
+    return a.c - b.c || b.ai + b.bi - a.ai - a.bi;
+}

packages/cspell-trie-lib/src/lib/suggestions/levenshtein.test.ts

@@ -0,0 +1,23 @@
+import { levenshteinDistance } from './levenshtein';
+
+describe('levenshtein', () => {
+    test.each`
+        left          | right        | expected
+        ${'abc'}      | ${'abc'}     | ${0}
+        ${'abc'}      | ${'ab'}      | ${1}
+        ${'abc'}      | ${''}        | ${3}
+        ${'kitten'}   | ${'sitting'} | ${3}
+        ${'Saturday'} | ${'Sunday'}  | ${3}
+        ${'ab'}       | ${'ba'}      | ${1}
+        ${'aba'}      | ${'bab'}     | ${2}
+        ${'abab'}     | ${'baba'}    | ${2}
+        ${'abab'}     | ${'ababa'}   | ${1}
+        ${'appear'}   | ${'apple'}   | ${3}
+        ${'appease'}  | ${'apple'}   | ${3}
+    `('levenshteinDistance "$left" vs "$right"', ({ left, right, expected }) => {
+        expect(levenshteinDistance(left, right)).toBe(expected);
+        expect(levenshteinDistance(right, left)).toBe(expected);
+    });
+});
+
+// cspell:ignore ababa