78 lines
2 KiB
Markdown
78 lines
2 KiB
Markdown
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# @tldraw/indices
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Welcome to **indices** by [tldraw](https://tldraw.dev). This library provides functions for features that rely on fractional indexing. It is based on the observable [Implementing Fractional Indexing](https://observablehq.com/@dgreensp/implementing-fractional-indexing) by [@DavidG](https://twitter.com/DavidG).
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Fractional indexing is a method for creating indices between other indices without running into precision errors. This is useful when items are modeled as object maps rather than as arrays.
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For example, imagine a stack of 5 cards:
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```ts
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const cards = {
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A: 0,
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B: 1,
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C: 2,
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D: 3,
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E: 4,
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}
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```
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In a naive implementation of indexing, moving card E to the "bottom" of the stack would mean changing every item in the map.
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```ts
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const cards = {
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A: 1,
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B: 2,
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C: 3,
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D: 4,
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E: 0, // <-- moved to back
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}
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```
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each with an index between `0` and `51`. In a naive implementation of indices, moving the top card (index `51`) to the bottom of the deck would mean changing its index to `0`, changing the previous bottom card's index to `1`, and so forth incrementing every other card's index by one.
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## Installation
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```bash
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npm i @tldraw/indices
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# or
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yarn add @tldraw/indices
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```
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## Usage
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### getIndexBetween
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Get an index between two other indices.
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### getIndexAbove
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Get an index above a given index.
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### getIndexBelow
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Get an index below a given index.
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### getIndicesBetween
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Get a number of indices between two indices.
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### getIndicesAbove
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Get a number of indices above a given index.
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### getIndicesBelow
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Get a number of indices below a given index.
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### getIndices
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Get an array of indices with a given length.
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### `sortByIndex`
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Sort an array of objects by their `index` property.
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## License
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The source code in this repository (as well as our 2.0+ distributions and releases) are currently licensed under Apache-2.0. These licenses are subject to change in our upcoming 2.0 release. If you are planning to use tldraw in a commercial product, please reach out at [hello@tldraw.com](mailto://hello@tldraw.com).
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