@visx/scale
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visx scale
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# @visx/scale
<a title="@visx/scale npm downloads" href="https://www.npmjs.com/package/@visx/scale">
<img src="https://img.shields.io/npm/dm/@visx/scale.svg?style=flat-square" />
</a>
## Installation
```sh
npm install --save @visx/scale
```
## Overview of scales
The `@visx/scale` package aims to provide a wrapper around existing `d3` scaling originally defined
in the [d3-scale](https://github.com/d3/d3-scale) package.
Scales are functions that help you map your data values to the physical pixel size that your graph
requires. For example, let's say you wanted to create a bar chart to show populations per country.
If you were to use a 1-to-1 scale (IE: 1 pixel per y value) your bar for the USA would be about
321.4 million pixels high!
Instead, you can tell `visx` a function to use that takes a data value (like your population per
country) and quantitatively maps to another dimensional space, like pixels.
For example, we could create a linear scale like this:
```js
const graphWidth = 500;
const graphHeight = 200;
const [minX, maxX] = getXMinAndMax();
const [minY, maxY] = getYMinAndMax();
const xScale = Scale.scaleLinear({
domain: [minX, maxX], // x-coordinate data values
range: [0, graphWidth], // svg x-coordinates, svg x-coordinates increase left to right
round: true,
});
const yScale = Scale.scaleLinear({
domain: [minY, maxY], // y-coordinate data values
// svg y-coordinates, these increase from top to bottom so we reverse the order
// so that minY in data space maps to graphHeight in svg y-coordinate space
range: [graphHeight, 0],
round: true,
});
// ...
const points = data.map((d, i) => {
const barHeight = graphHeight - yScale(d.y);
return <Shape.Bar height={barHeight} y={graphHeight - barHeight} />;
});
```
## Different types of scales
### Band scale
[Original d3 docs](https://github.com/d3/d3-scale/blob/master/README.md#_band)
Example:
```js
const scale = Scale.scaleBand({
/*
range,
round,
domain,
padding,
nice = false
*/
});
```
### Linear scale
[Original d3 docs](https://github.com/d3/d3-scale/blob/master/README.md#scaleLinear)
Example:
```js
const scale = Scale.scaleLinear({
/*
range,
round,
domain,
nice = false,
clamp = false,
*/
});
```
### Log scale
[Original d3 docs](https://github.com/d3/d3-scale/blob/master/README.md#scaleLog)
Example:
```js
const scale = Scale.scaleLog({
/*
range,
round,
domain,
base,
nice = false,
clamp = false,
*/
});
```
**Important note:** As log(0) = -∞, a log scale domain must be strictly-positive or
strictly-negative; the domain must not include or cross zero.
### Radial scale
[Original d3 docs](https://github.com/d3/d3-scale/blob/master/README.md#scaleRadial)
Example:
```js
const scale = Scale.scaleRadial({
/*
range,
round,
domain,
nice = false,
clamp = false,
*/
});
```
### Ordinal scale
[Original d3 docs](https://github.com/d3/d3-scale/blob/master/README.md#scaleOrdinal)
Example:
```js
const scale = Scale.scaleOrdinal({
/*
range,
domain,
unknown,
*/
});
```
### Point scale
[Original d3 docs](https://github.com/d3/d3-scale/blob/master/README.md#scalePoint)
Example:
```js
const scale = Scale.scalePoint({
/*
range,
round,
domain,
padding,
align,
nice = false,
*/
});
```
### Power scale
[Original d3 docs](https://github.com/d3/d3-scale/blob/master/README.md#scalePow)
Example:
```js
const scale = Scale.scalePower({
/*
range,
round,
domain,
exponent,
nice = false,
clamp = false,
*/
});
```
### Square Root scale
[Original d3 docs](https://github.com/d3/d3-scale#scaleSqrt)
Example:
```js
// No need to set the exponent, It is always 0.5
const scale = Scale.scaleSqrt({
/*
range,
round,
domain,
nice = false,
clamp = false,
*/
});
```
### Time scale
[Original d3 docs](https://github.com/d3/d3-scale/blob/master/README.md#scaleTime)
Example:
```js
const scale = Scale.scaleTime({
/*
range,
round,
domain,
nice = false,
clamp = false,
*/
});
```
You also can scale time with Coordinated Universal Time via `scaleUtc`.
Example:
```js
const scale = Scale.scaleUtc({
/*
range,
round,
domain,
nice = false,
clamp = false,
*/
});
```
### Color Scales
D3 scales offer the ability to map points to colors. You can use
[`d3-scale-chromatic`](https://github.com/d3/d3-scale-chromatic) in conjunction with visx's
`scaleOrdinal` to make color scales.
You can install `d3-scale-chromatic` with npm:
```sh
npm install --save d3-scale-chromatic
```
You create a color scale like so:
```js
import { scaleOrdinal } from '@visx/scale';
import { schemeSet1 } from 'd3-scale-chromatic';
const colorScale = scaleOrdinal({
domain: arrayOfThings,
range: schemeSet1,
});
```
This generates a color scale with the following colors:
There are a number of other
[categorical color schemes](https://github.com/d3/d3-scale-chromatic/blob/master/README.md#categorical)
available, along with other continuous color schemes.