# level-merged-stream
> [](https://travis-ci.org/coinative/level-merged-stream) [](https://coveralls.io/r/c
Latest version **0.0.2** (published 2014-06-16) · MIT license · 0 weekly downloads
## Install
```sh
npm install level-merged-stream
pnpm add level-merged-stream
yarn add level-merged-stream
bun add level-merged-stream
```
## Health
**Score 15/100 (F)** — status: abandoned.
Positive: no vulnerabilities.
Warnings: low downloads; no types; no esm support; pre 1.0.
Negative: abandoned; low maintenance score.
## Facts
| | |
|---|---|
| Version | 0.0.2 |
| Published | 2014-06-16 |
| First published | 2014-06-16 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | none |
| Module format | CommonJS |
| Dependencies | 5 |
| Known vulnerabilities | 0 |
| Install scripts | no |
| Author | Ben Shepheard |
| Maintainers | hypergeometric |
## Links
- npm: https://www.npmjs.com/package/level-merged-stream
- Repository: https://github.com/coinative/level-merged-stream
- Issues: https://github.com/coinative/level-merged-stream/issues
- npm.io page: https://npm.io/package/level-merged-stream
## Dependencies (5)
- [xtend](https://npm.io/package/xtend.md) ^3.0.0
- [through2](https://npm.io/package/through2.md) ^0.4.2
- [limit-stream](https://npm.io/package/limit-stream.md) ^2.0.0
- [offset-stream](https://npm.io/package/offset-stream.md) 0.0.0
- [mergesort-stream](https://npm.io/package/mergesort-stream.md) 0.0.3
## Recent versions
- 0.0.2 (latest) — 2014-06-16
- 0.0.1 — 2014-06-16
## README
# level-merged-stream
[](https://travis-ci.org/coinative/level-merged-stream) [](https://coveralls.io/r/coinative/level-merged-stream?branch=master)
A [LevelUP](https://github.com/rvagg/node-levelup) plugin to merge multiple ranges into a single sorted stream using a subkey for ordering. Useful when doing range queries against multiple key-based secondary indexes. Supports standard LevelUP stream options and naïve pagination via a `skip` option.
## Install
Not currently hosted on npmjs.org. Take this module as a git dependency via:
```
npm install level-merged-stream
```
## Usage
Given a LevelUP instance `db`:
```js
var mergedStream = require('level-merged-stream');
db = mergedStream(db);
```
## API
* db.createMergedReadStream()
* db.createMergedKeyStream()
* db.createMergedValueStream()
--------------------------------------------------------
### db.createMergedReadStream([options])
As per [`db.createReadStream()`](https://github.com/rvagg/node-levelup/blob/master/README.md#createReadStream) but with the following additional options:
* `'ranges'` *(array)*: The `start`/`end` ranges as you'd provide to `createReadStream`. Each range is streamed and merged according to the value privided by `subkey`. Each range must be ordered by `subkey`, i.e. any range prefix must be constant for the entire range for overall ordering to be consistent.
* `'subkey'` *(function, default: identity)*: Selects the subkey from the key that is used for ordering the results.
* `'comparator'` *(function, default: primitive comparison)*: A subkey comparator function if primitive comparison is insufficient, .e.g. for Buffers or custom keys.
* `'dedupe'` *(boolean/function, default: `false`)*: If `true`, when two or more subkeys are considered equal, only the first result will be streamed. The key and/or value returned could come from any underlying range stream. If a function, it should return `true` if two keys passed are considered equal for deduplication purposes.
* `'skip'` *(number, default: `0`)*: The number of results to skip in the merged stream. Useful for pagination when also using `limit`.
--------------------------------------------------------
### db.createMergedKeyStream([options])
As per [`db.createKeyStream()`](https://github.com/rvagg/node-levelup/blob/master/README.md#createKeyStream) this streams only the keys.
--------------------------------------------------------
### db.createMergedValueStream([options])
As per [`db.createValueStream()`](https://github.com/rvagg/node-levelup/blob/master/README.md#createValueStream) this streams only the values.
--------------------------------------------------------
## Example
`examples/readme.js`:
```js
var path = require('path');
var level = require('level');
var mergedStream = require('level-merged-stream');
var location = path.join(__dirname, '/.db');
var db = level(location);
db = mergedStream(db);
db.batch()
.put('a1', '1')
.put('b2', '2')
.put('c3', '3')
.put('d4', '4')
.put('a5', '5')
.put('b6', '6')
.put('c7', '7')
.put('d8', '8')
.write(function () {
db.mergedReadStream({
// Only stream the 'a's and 'c's
ranges: [
{ start: 'a', end: 'b' },
{ start: 'c', end: 'd' }
],
// Ignore the first character for sorting
subkey: function (key) {
return key.slice(1);
},
skip: 1,
limit: 2
})
.on('data', console.log)
.on('end', function () {
db.close(function () {
level.destroy(location);
});
});
});
```
Output:
```
{ key: 'c3', value: '3' }
{ key: 'a5', value: '5' }
```
## License
MIT
---
_Source: https://npm.io/package/level-merged-stream · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._