https://github.com/se2p/pq-distance
Approximate Tree-Edit Distance for Node.js
https://github.com/se2p/pq-distance
Last synced: 5 months ago
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Approximate Tree-Edit Distance for Node.js
- Host: GitHub
- URL: https://github.com/se2p/pq-distance
- Owner: se2p
- License: gpl-3.0
- Created: 2024-10-28T07:43:01.000Z (over 1 year ago)
- Default Branch: main
- Last Pushed: 2025-10-24T07:05:28.000Z (9 months ago)
- Last Synced: 2025-10-24T08:35:48.590Z (9 months ago)
- Language: TypeScript
- Size: 152 KB
- Stars: 0
- Watchers: 0
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# pq-distance: Approximate Tree-Edit Distance for Node.js
[](https://www.npmjs.com/package/@se2p/pq-distance)
Modern TypeScript implementation of pq-gram distance, an efficient approximation for tree-edit distance. Algorithm based
on academic papers[^1][^2] and thesis[^5]. Implementation ported from LitterBox[^3]. Node.js API inspired by jqgram[^4].
## Installation
The package can be installed as `@se2p/pq-distance` from npm:
```bash
npm install @se2p/pq-distance
```
## Usage
The package exports two functions function `pqDistance` and `pqDistanceWindowed`:
```javascript
const {pqDistance, pqDistanceWindowed} = require("@se2p/pq-distance");
```
TypeScript users can also import the `PQTree`, `PQOpts` and `PQWindowedOpts` types:
```typescript
import {pqDistance, pqDistanceWindowed, PQTree, PQOpts, PQWindowedOpts} from "@se2p/pq-distance";
```
Example trees:
```
a a
/|\ /|\
t1: a b c t2: a b c
/ \ / \
e b e x
```
Arbitrary tree-representations are supported. Provide two functions `getLabel()` to extract the label as string from a
node, and `getChildren()` that returns a node's children in an array.
For example:
```typescript
const t1 = {
label: 'a',
children: [
{
label: 'a',
children: [
{
label: 'e',
children: []
},
{
label: 'b',
children: []
}
]
},
{
label: 'b',
children: []
},
{
label: 'c',
children: []
}
]
};
const t2 = {
node: 'A',
child: [
{
node: 'A',
child: [
{node: 'E'},
{node: 'B'}
]
},
{node: 'B'},
{node: 'X'}
]
};
```
To compute the pq-gram distance between `t1` and `t2`, pass them as `PQTree` objects to `pqDistance()`:
```typescript
const tree1: PQTree = {
root: t1,
getLabel: ({label}) => label,
getChildren: ({children}) => children
};
const tree2: PQTree = {
root: t2,
getLabel: (n) => n.node.toLowerCase(),
getChildren: (n) => n.child ?? []
};
```
Finally:
```typescript
const opts: PQOpts = {p: 2, q: 3}; // default values
pqDistance(tree1, tree2, opts); // 0.3076923076923077
```
The use is analogous for the windowed pq-gram distance:
```typescript
const opts: PQWindowedOpts = {p: 2, w: 3}; // default values
pqDistanceWindowed(tree1, tree2, opts); // 0.3125
```
The object `opts` sets the `p` and `q` values for `pqDistance`, and may be omitted to use the default values
`p=2` and `q=3`. In case of `pqDistanceWindowed`, you must use `w` instead of `q`. The default values are
`p=2` and `w=3`. Please refer to the academic papers how they affect the distance value.
## License
pq-distance 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.
pq-distance 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.
[^1]: Nikolaus Augsten, Michael H. Böhlen, and Johann Gamper. 2005. Approximate Matching of Hierarchical Data Using
pq-Grams. In Proceedings of the 31st International Conference on Very Large Data Bases, Trondheim, Norway, August 30
– September 2, 2005
[^2]: https://github.com/DatabaseGroup/apted
[^3]: https://github.com/se2p/LitterBox
[^4]: https://github.com/hoonto/jqgram
[^5]: https://vbn.aau.dk/en/publications/approximate-matching-of-hierarchial-data