npm package: @nebula.js/sn-sankey-chart
Description: A flow diagram visually emphasizing major transfers or flows within defined system boundaries.
Author: QlikTech International AB
Latest version: 1.13.0

# @nebula.js/sn-sankey-chart

The Sankey chart is a flow chart which visually emphasizes major transfers or flows within defined system boundaries. The width of the chart arrows is shown proportionally to the flow quantity.

- A minimum of two dimensions and one measure is required.
  You can use up to five dimensions, but only one measure.
- The dimensions do not need to be of equal size on each side of the diagram.
- You can use the dimension values to set the color of the flows in the chart.
- Link colors can be based on source or target anchor.

## Requirements

Requires `@nebula.js/stardust` version `1.2.0` or later.

## Installing

If you use npm: `npm install @nebula.js/sn-sankey-chart`. You can also load through the script tag directly from [https://unpkg.com](https://unpkg.com/@nebula.js/sn-sankey-chart).

## Usage

```js
import { embed } from '@nebula.js/stardust';
import sankey from '@nebula.js/sn-sankey-chart';

// 'app' is an enigma app model
const nuked = embed(app, {
  types: [
    {
      // register sankey chart
      name: 'sankey',
      load: () => Promise.resolve(sankey),
    },
  ],
});

nuked.render({
  element,
  type: 'sankey',
  fields: ['Region', 'Product Group', 'Product Type', 'Product Line', '=Sum(Margin)'],
  // overrides default properties
  properties: {
    node: {
      padding: 0.2,
      width: 0.3,
    },
    link: {
      opacity: 0.5,
      shadow: false,
      color: 3,
      colorBy: 'custom',
    },
  },
});
```

## More examples

### Node and link colors

You can change the node colors of each dimension value.
The color should be a valid CSS color.

The colors of chart links are based on either the source or target anchors.
To apply the source or target anchor color to chart links
either use the string `='SOURCE'` or `='TARGET'`.
You can also select a separate color by entering a color code string.
The color should be a valid CSS color.

```js
nuked.render({
  element: document.querySelector('.object'),
  type: 'sankeyChart',
  properties: {
    node: {
      padding: 0.1,
      width: 0.7,
    },
    qHyperCubeDef: {
      qDimensions: [
        {
          qDef: {
            qFieldDefs: ['Region'],
          },
          qAttributeExpressions: [
            {
              qExpression: "if(Sum(total<Region> Margin) > 4500000, '#53ac94', '#ac536b')",
            },
          ],
        },
        {
          qDef: {
            qFieldDefs: ['Product Group'],
          },
          qAttributeExpressions: [
            {
              qExpression: "'#28bad7'",
            },
          ],
        },
      ],
      qMeasures: [
        {
          qDef: {
            qDef: 'Sum(Margin)',
          },
          qAttributeExpressions: [
            {
              qExpression: "if(Sum(Margin) > 300000, '#53ac94', '#ac536b')",
            },
          ],
        },
      ],
      qInitialDataFetch: [
        {
          qLeft: 0,
          qTop: 0,
          qWidth: 6,
          qHeight: 1000,
        },
      ],
    },
  },
});
```

### Links colored based on their source

```js
nuked.render({
  element: document.querySelector('.object'),
  type: 'sankeyChart',
  fields: ['Product Group', 'Product Type'],
  properties: {
    qHyperCubeDef: {
      qDimensions: [
        {
          qDef: {
            qFieldDefs: ['Region'],
          },
          qAttributeExpressions: [
            {
              qExpression: "if(Sum(total<Region> Margin) > 4500000, '#53ac94', '#ac536b')",
            },
          ],
        },
      ],
      qMeasures: [
        {
          qDef: {
            qDef: 'Sum(Margin)',
          },
          qAttributeExpressions: [
            {
              qExpression: "='SOURCE'",
            },
          ],
        },
      ],
      qInitialDataFetch: [
        {
          qLeft: 0,
          qTop: 0,
          qWidth: 6,
          qHeight: 1000,
        },
      ],
    },
  },
});
```

## Sankey chart plugins

A plugin can be passed into a Sankey chart to add or modify its capability
or visual appearance.
A plugin needs to be defined before it can be rendered together with the chart.

```js
// Step 1: define the plugin

// Adding a text component
const textPlugin = {
  info: {
    name: 'text-plugin',
    type: 'component-definition',
  },
  fn: ({ layout, keys }) => {
    const componentDefinition = {
      type: 'text',
      key: 'my-text',
      text: 'Sales of Clothes in Different Areas',
      layout: { dock: 'top' },
    };
    return componentDefinition;
  },
};

// Step 2: passing the plugin definition into the render function

// Rendering a Sankey chart with plugins
nuked.render({
  element: document.getElementById('object'),
  type: 'sn-sankey-chart',
  fields: ['CategoryName', 'Region', '=Sum(Sales)'],
  plugins: [textPlugin], // eslint-disable-line no-undef
});
```

The plugin definition is an object, with two properties `info` and `fn`.
The `fn` returns a `picasso.js` component. To build this component,
some important chart internals are passed into the argument object of `fn`.

```js
// Structure of the argument object of fn
const pluginArgs = {
  layout,
  keys: {
    SCALE: { DIMENSIONS },
    COMPONENT: { LABELS_TITLES, LABELS },
  },
};
```

With plugins, you can either add new components or modify existing components
of the Sankey chart.

### Add new components

The new component can be a standard Picasso component
or a custom Picasso component. Here we demo a standard label component
which add a label at the top center of the chart.

```js
// Adding a text component
const textPlugin = {
  info: {
    name: 'text-plugin',
    type: 'component-definition',
  },
  fn: ({ layout, keys }) => {
    const componentDefinition = {
      type: 'text',
      key: 'my-text',
      text: 'Sales of Clothes in Different Areas',
      layout: { dock: 'top' },
    };
    return componentDefinition;
  },
};
```

### Modify existing components

As an example, the appearance of the labels can be
modified by plugins.

To overide an existing component, `fn` should returns a `picasso.js` component
that has the same `key` as the existing component (`keys.COMPONENT.LABELS` in
this example)

```js
// Modifying the look of the labels
const labelsPlugin = {
  info: {
    name: 'labels-plugin',
    type: 'component-definition',
  },
  fn: ({ keys, layout }) => {
    const componentDefinition = {
      type: 'labels',

      // Provide the same name as the exisiting component to override it
      key: keys.COMPONENT.LABELS,
      settings: {
        sources: [
          {
            component: 'san',
            selector: '.labelCenter',
            strategy: {
              type: 'rows',
              settings: {
                align: 0.5,
                justify: 0.5,
                padding: 4,
                labels: [{}, {}],
              },
            },
          },
          {
            component: 'san',
            selector: '.labelLeft',
            strategy: {
              type: 'rows',
              settings: {
                align: 0,
                justify: 0.5,
                padding: 4,
                fontFamily: 'Helvetica',
                fontSize: '14',
                fill: 'darkgreen',
              },
            },
          },
          {
            component: 'san',
            selector: '.labelRight',
            strategy: {
              type: 'rows',
              settings: {
                align: 1,
                justify: 0.5,
                padding: 4,
                fontFamily: 'Helvetica',
                fontSize: '14',
                fill: 'darkred',
              },
            },
          },
        ],
      },
    };
    return componentDefinition;
  },
};
```

### Plugins disclaimer

- The plugins API is still experimental.
- We can not guarantee our charts to be compatible with all different settings, especially when modifying existing components.