# Yahoo! UI Library

### DataTable Widget 2.9.0

Yahoo! UI Library > datatable > YAHOO.widget.ColumnSet
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## Class YAHOO.widget.ColumnSet - uses YAHOO.util.EventProvider

The ColumnSet class defines and manages a DataTable's Columns, including nested hierarchies and access to individual Column instances.

### Constructor

YAHOO.widget.ColumnSet `( aDefinitions )`

Parameters:
  `aDefinitions <Object[]>` Array of object literals that define cells in the THEAD.

### Properties

#### _aDefinitions - `private Object[]`

Array of object literal Column definitions passed to the constructor.

#### _sId - `private String`

Unique instance name.

#### ColumnSet._nCount - `private static Number`

Internal class variable to index multiple ColumnSet instances.

#### flat - `YAHOO.widget.Column[]`

Flattened representation of all Columns.
Default Value: []

#### headers - `String[]`

ID index of nested parent hierarchies for HEADERS accessibility attribute.
Default Value: []

#### keys - `YAHOO.widget.Column[]`

Array of Columns that map one-to-one to a table column.
Default Value: []

#### tree - `YAHOO.widget.Column[]`

Top-down tree representation of Column hierarchy.

#### Properties inherited from YAHOO.util.EventProvider:

`__yui_events, __yui_subscribers`

### Methods

#### _init

`private void _init ( aDefinitions )`
Initializes ColumnSet instance with data from Column definitions.

Parameters:
  `aDefinitions <Object[]>` Array of object literals that define cells in the THEAD .

#### getColumn

`YAHOO.widget.Column getColumn ( column )`
Returns Column instance with given key or ColumnSet key index.

Parameters:
  `column <String | Number>` Column key or ColumnSet key index.

Returns: `YAHOO.widget.Column`
  Column instance.

#### getColumnById

`YAHOO.widget.Column getColumnById ( column )`
Returns Column instance with given ID.

Parameters:
  `column <String>` Column ID.

Returns: `YAHOO.widget.Column`
  Column instance.

#### getDefinitions

`Object[] getDefinitions ( )`
Public accessor to the definitions array.

Returns: `Object[]`
  Array of object literal Column definitions.

#### getDescendants

`Array getDescendants ( )`
Public accessor returns array of given Column's desendants (if any), including itself.

Returns: `Array`
  Array including the Column itself and all descendants (if any).

#### getId

`String getId ( )`
Returns unique name of the ColumnSet instance.

Returns: `String`
  Unique name of the ColumnSet instance.

#### toString

`String toString ( )`
ColumnSet instance name, for logging.

Returns: `String`
  Unique name of the ColumnSet instance.

#### Methods inherited from YAHOO.util.EventProvider:

`createEvent, fireEvent, hasEvent, subscribe, unsubscribe, unsubscribeAll`

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