> ## Documentation Index
> Fetch the complete documentation index at: https://docs.arc.cdata.com/llms.txt
> Use this file to discover all available pages before exploring further.

# arc:map

> Use arc:map to map attributes in one item to attributes in another item, reading from a source item and writing to a destination item with new names.

export const siteNameShort = "Arc";

Use the `arc:map` keyword to map attributes in one item to attributes in another item. Attributes are read from one item and written to another with the new names specified in the map string. The `arc:map` keyword does not clear the destination item; it simply adds new attributes to it. If an attribute exists in the destination item, it is overwritten, and other attributes remain as they were.

## Parameters

* **to**: The name of the item into which attributes are written.
* **from**: The name of the item from which attributes are read.
* **map**: A list of attribute names that specify the attribute names in the destination item, followed by the attribute names in the source item. For example, you can map attributes with one prefix to attributes with another prefix by using the syntax below:

  `customer:\* = soap:\*`

  Any characters that are not valid attribute names are ignored and used to demarcate the end of a name.

## Control Attributes

None

## Examples

Map three attributes: The map is a succession of the `to` attribute name followed by the `from` attribute name.

```xml theme={null}
<arc:set item="item1" attr="var1" value="x"/>
<arc:set item="item1" attr="var2" value="y"/>
<arc:set item="item2" attr="attr1" value="z"/>
<arc:map to="item2" from="item1" map="attr1=var1, attr2=var2"/>
```

In this example, the `var1` and `var2` attributes of `item1` are mapped to the `attr1` and `attr2` attributes of `item2`. The `attr1` attribute, which is set to the value `z` in `item2`, is overwritten with `x`, the value of `var1` from `item1`. The `attr2` attribute, which does not exist in `item2`, is created and set to `y` (the value of `var2` in `item1`).

You can map multiple attributes from items with one prefix to items with a different prefix. This is useful when changing the prefix from application prefixes (for example, `soap:*`) to business domain prefixes (for example, `customer:*`). The following example creates a mapping from all `soap:*` attributes in the `soapout` item to attributes prefixed with `customer:*` in the `customer` item:

```xml theme={null}
<arc:map from="soapout" to="customer" map="customer:* = soap:*"/>
```

Copy all attributes from one item to another item:

```xml theme={null}
<arc:map from="copyfrom" to="copyto" map="* = *"/>
```

## See Also

* [arc:set](./op-arc-set): Set the attributes of an item.