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Initial commit; v1.0.0

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Sven Slootweg vor 4 Jahren
Commit 90c3a2a083

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# generate-lookup-table
Generates a (fast!) lookup table or index from any array of items.
__When to use this:__ When you might otherwise be looping through an array *many times* (eg. using `Array#find`), trying to locate an item(s) with a particular property.
If you'd otherwise only loop through the array *once*, it's probably faster *not* to use this library, and just do the loop - building a lookup table, while still quite fast in the bigger picture, takes time.
## License, donations, and other boilerplate
Licensed under either the [WTFPL](http://www.wtfpl.net/txt/copying/) or [CC0](https://creativecommons.org/publicdomain/zero/1.0/), at your choice. In practice, that means it's more or less public domain, and you can do whatever you want with it. Giving credit is *not* required, but still very much appreciated! I'd love to [hear from you](mailto:admin@cryto.net) if this module was useful to you.
Creating and maintaining open-source modules is a lot of work. A donation is also not required, but much appreciated! You can donate [here](http://cryto.net/~joepie91/donate.html).
## Usage
```js
"use strict";
const generateLookupTable = require("generate-lookup-table");
// Thanks to https://gist.github.com/nanotaboada/6396437 for the sample data!
let items = [
{ name: "Eloquent JavaScript, Second Edition", tags: [ "javascript", "No Starch Press" ] },
{ name: "Learning JavaScript Design Patterns", tags: [ "javascript", "O'Reilly Media" ] },
{ name: "Speaking JavaScript", tags: [ "javascript", "O'Reilly Media" ] },
{ name: "Programming JavaScript Applications", tags: [ "javascript", "O'Reilly Media" ] },
{ name: "Understanding ECMAScript 6", tags: [ "javascript", "No Starch Press" ] },
{ name: "You Don't Know JS", tags: [ "javascript", "O'Reilly Media" ] },
{ name: "Git Pocket Guide", tags: [ "git", "O'Reilly Media" ] },
{ name: "Designing Evolvable Web APIs with ASP.NET", tags: [ "asp.net", "O'Reilly Media" ] },
];
let lookupTable = generateLookupTable(items, (item) => item.tags);
console.log(lookupTable.get("git"));
/* Output:
[ { name: 'Git Pocket Guide', tags: [ 'git', 'O\'Reilly Media' ] } ]
*/
console.log(lookupTable.get("No Starch Press"));
/* Output:
[ { name: 'Eloquent JavaScript, Second Edition',
tags: [ 'javascript', 'No Starch Press' ] },
{ name: 'Understanding ECMAScript 6',
tags: [ 'javascript', 'No Starch Press' ] } ]
*/
```
## API
### generateLookupTable(items, keyFunction)
Generates a lookup table for the given set of `items`, using the `keyFunction` to determine what key(s) each item should be registered for.
- __items:__ The array of items to index.
- __keyFunction(item):__ A function that, given an `item` as its argument, returns the key(s) for that item. The function may return either a single key, an array of them, or nothing at all.
Returns a `Map` that maps from a key (as returned from the `keyFunction`) to all items that returned that particular key.
## Changelog
### v1.0.0 (February 21, 2020)
Initial release.

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"use strict";
const generateLookupTable = require("./");
// Thanks to https://gist.github.com/nanotaboada/6396437 for the sample data!
let items = [
{ name: "Eloquent JavaScript, Second Edition", tags: [ "javascript", "No Starch Press" ] },
{ name: "Learning JavaScript Design Patterns", tags: [ "javascript", "O'Reilly Media" ] },
{ name: "Speaking JavaScript", tags: [ "javascript", "O'Reilly Media" ] },
{ name: "Programming JavaScript Applications", tags: [ "javascript", "O'Reilly Media" ] },
{ name: "Understanding ECMAScript 6", tags: [ "javascript", "No Starch Press" ] },
{ name: "You Don't Know JS", tags: [ "javascript", "O'Reilly Media" ] },
{ name: "Git Pocket Guide", tags: [ "git", "O'Reilly Media" ] },
{ name: "Designing Evolvable Web APIs with ASP.NET", tags: [ "asp.net", "O'Reilly Media" ] },
];
let lookupTable = generateLookupTable(items, (item) => item.tags);
console.log(lookupTable.get("git"));
/* Output:
[ { name: 'Git Pocket Guide', tags: [ 'git', 'O\'Reilly Media' ] } ]
*/
console.log(lookupTable.get("No Starch Press"));
/* Output:
[ { name: 'Eloquent JavaScript, Second Edition',
tags: [ 'javascript', 'No Starch Press' ] },
{ name: 'Understanding ECMAScript 6',
tags: [ 'javascript', 'No Starch Press' ] } ]
*/

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"use strict";
module.exports = function generateLookupTable(items, getKey) {
let lookupTable = new Map();
function setItem(key, value) {
// TODO: Add a fast path for unique keys (no array wrapping), so that the index can contain both single items and arrays?
if (lookupTable.has(key)) {
lookupTable.get(key).push(value);
} else {
lookupTable.set(key, [ value ]);
}
}
items.forEach((item) => {
let key = getKey(item);
if (key != null) {
if (Array.isArray(key)) {
// This item should be available under multiple keys
for (let keyItem of key) {
setItem(keyItem, item);
}
} else {
setItem(key, item);
}
}
});
return lookupTable;
};

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{
"name": "generate-lookup-table",
"description": "Generates a (fast!) lookup table or index from any array of items.",
"keywords": [ "index", "lookup table", "map", "generate", "generator" ],
"version": "1.0.0",
"main": "index.js",
"repository": "https://git.cryto.net/joepie91/generate-lookup-table.git",
"author": "Sven Slootweg <admin@cryto.net>",
"license": "WTFPL OR CC0-1.0"
}
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