# Pack Transform

The **pack** transform computes an enclosure diagram that uses containment (nesting) to represent a hierarchy. The size of the leaf circles encodes a quantitative dimension of the data. The enclosing circles show the approximate cumulative size of each subtree, but due to wasted space there is some distortion; only the leaf nodes can be compared accurately.

Internally, this transform processes a collection of special tree node objects generated by an upstream nest or stratify transform. The original input data object can be accessed under the `data`

field of these tree node objects. This transform uses the d3-hierarchy library.

## Example

## Transform Parameters

Property | Type | Description |
---|---|---|

field | Field | The data field corresponding to a numeric value for the node. The sum of values for a node and all its descendants is available on the node object as the `value` property. If radius is `null` , this field determines the node size. |

sort | Compare | A comparator for sorting sibling nodes. The inputs to the comparator are tree node objects, not input data objects. |

size | Number[ ] | The size of the layout, provided as a [width, height] array. |

radius | Field | An explicit node radius to use. If `null` (the default), the radius of each leaf circle is derived from the field value. |

padding | Number | The approximate padding to include between packed circles (default `0` ). |

as | String[ ] | The output fields at which to write the layout results. The default is `["x", "y", "r", "depth", "children"]` , where `x` and `y` are the layout coordinates, `r` is the node radius, `depth` is the tree depth, and `children` is the count of a node’s children in the tree. |

## Usage

```
{
"type": "pack",
"field": "value",
"padding": 4,
"size": [{"signal": "width"}, {"signal": "height"}]
}
```

Computes a pack layout with `4`

pixel padding between nodes, using the full width and height of the view. Leaf nodes are sized proportionally to the `value`

field.