# DataSet

## Contents

- Overview
- Example
- Construction
- Methods
- Properties
- Subscriptions
- Data Manipulation
- Data Selection

## Overview

Vis.js comes with a flexible DataSet, which can be used to hold and manipulate unstructured data and listen for changes in the data. The DataSet is key/value based. Data items can be added, updated and removed from the DatSet, and one can subscribe to changes in the DataSet. The data in the DataSet can be filtered and ordered, and fields (like dates) can be converted to a specific type. Data can be normalized when appending it to the DataSet as well.

## Example

The following example shows how to use a DataSet.

    // create a DataSet
    var options = {};
    var data = new vis.DataSet(options);

    // add items
    // note that the data items can contain different properties and data formats
    data.add([
      {id: 1, text: 'item 1', date: new Date(2013, 6, 20), group: 1, first: true},
      {id: 2, text: 'item 2', date: '2013-06-23', group: 2},
      {id: 3, text: 'item 3', date: '2013-06-25', group: 2},
      {id: 4, text: 'item 4'}
    ]);

    // subscribe to any change in the DataSet
    data.on('*', function (event, properties, senderId) {
      console.log('event', event, properties);
    });

    // update an existing item
    data.update({id: 2, group: 1});

    // remove an item
    data.remove(4);

    // get all ids
    var ids = data.getIds();
    console.log('ids', ids);

    // get a specific item
    var item1 = data.get(1);
    console.log('item1', item1);

    // retrieve a filtered subset of the data
    var items = data.get({
      filter: function (item) {
        return item.group == 1;
      }
    });
    console.log('filtered items', items);

    // retrieve formatted items
    var items = data.get({
      fields: ['id', 'date'],
      type: {
        date: 'ISODate'
      }
    });
    console.log('formatted items', items);

## Construction

A DataSet can be constructed as:

    var data = new vis.DataSet([data] [, options])

After construction, data can be added to the DataSet using the methods `add` and `update`, as described in section Data Manipulation.

The parameter `data` is optional and is an Array with items.

The parameter `options` is optional and is an object which can contain the following properties:

Name | Type | Default value | Description
--- | --- | --- | ---
fieldId | String | "id" | The name of the field containing the id of the items. When data is fetched from a server which uses some specific field to identify items, this field name can be specified in the DataSet using the option `fieldId`. For example CouchDB uses the field `"_id"` to identify documents.
type | Object.<String, String> | none | An object containing field names as key, and data types as value. By default, the type of the properties of items are left unchanged. Item properties can be normalized by specifying a field type. This is useful for example to automatically convert stringified dates coming from a server into JavaScript Date objects. The available data types are listed in section Data Types.
queue | Object | boolean | none | Queue data changes ('add', 'update', 'remove') and flush them at once. The queue can be flushed manually by calling `DataSet.flush()`, or can be flushed after a configured delay or maximum number of entries. When `queue` is true, a queue is created with default options. Options can be specified by providing an object: `delay: number` The queue will be flushed automatically after an inactivity of this delay in milliseconds. Default value is `null`. `max: number` When the queue exceeds the given maximum number of entries, the queue is flushed automatically. Default value is `Infinity`.

## Methods

DataSet contains the following methods.

Method | Return Type | Description
--- | --- | ---
add(data [, senderId]) | Number[] | Add one or multiple items to the DataSet. `data` can be a single item or an array with items. Adding an item will fail when there already is an item with the same id. The function returns an array with the ids of the added items. See section Data Manipulation.
clear([senderId]) | Number[] | Clear all data from the DataSet. The function returns an array with the ids of the removed items.
distinct(field) | Array | Find all distinct values of a specified field. Returns an unordered array containing all distinct values. If data items do not contain the specified field are ignored.
flush() | none | Flush queued changes. Only available when the DataSet is configured with the option `queue`, see section Construction.
forEach(callback [, options]) | none | Execute a callback function for every item in the dataset. The available options are described in section Data Selection.
get([options] [, data]) get(id [,options] [, data]) get(ids [, options] [, data]) | Object | Array | Get a single item, multiple items, or all items from the DataSet. Usage examples can be found in section Getting Data, and the available `options` are described in section Data Selection. When no item is found, `null` is returned when a single item was requested, and and empty Array is returned in case of multiple id's.
getDataSet() | DataSet | Get the DataSet itself. In case of a DataView, this function does not return the DataSet to which the DataView is connected.
getIds([options]) | Number[] | Get ids of all items or of a filtered set of items. Available `options` are described in section Data Selection, except that options `fields` and `type` are not applicable in case of `getIds`.
map(callback [, options]) | Array | Map every item in the DataSet. The available options are described in section Data Selection.
max(field) | Object | null | Find the item with maximum value of specified field. Returns `null` if no item is found.
min(field) | Object | null | Find the item with minimum value of specified field. Returns `null` if no item is found.
off(event, callback) | none | Unsubscribe from an event, remove an event listener. See section Subscriptions.
on(event, callback) | none | Subscribe to an event, add an event listener. See section Subscriptions.
remove(id [, senderId]) remove(ids [, senderId]) | Number[] | Remove one or multiple items by id or by the items themselves. Returns an array with the ids of the removed items. See section Data Manipulation.
setOptions(options) | none | Set options for the DataSet. Available options: `queue` Queue data changes ('add', 'update', 'remove') and flush them at once. The queue can be flushed manually by calling `DataSet.flush()`, or can be flushed after a configured delay or maximum number of entries. When `queue` is true, a queue is created with default options. When `queue` is false, an existing queue will be flushed and removed. Options can be specified by providing an object: `delay: number` The queue will be flushed automatically after an inactivity of this delay in milliseconds. Default value is `null`. `max: number` When the queue exceeds the given maximum number of entries, the queue is flushed automatically. Default value is `Infinity`.
update(data [, senderId]) | Number[] | Update on ore multiple existing items. `data` can be a single item or an array with items. When an item doesn't exist, it will be created. Returns an array with the ids of the removed items. See section Data Manipulation.

## Properties

DataSet contains the following properties.

Property | Type | Description
--- | --- | ---
length | Number | The number of items in the DataSet.

## Subscriptions

One can subscribe on changes in a DataSet. A subscription can be created using the method `on`, and removed with `off`.

    // create a DataSet
    var data = new vis.DataSet();

    // subscribe to any change in the DataSet
    data.on('*', function (event, properties, senderId) {
      console.log('event:', event, 'properties:', properties, 'senderId:', senderId);
    });

    // add an item
    data.add({id: 1, text: 'item 1'});              // triggers an 'add' event
    data.update({id: 1, text: 'item 1 (updated)'}); // triggers an 'update' event
    data.remove(1);                                 // triggers an 'remove' event

### On

Subscribe to an event.

Syntax:

    DataSet.on(event, callback)

Where:

- `event` is a String containing any of the events listed in section Events.
- `callback` is a callback function which will be called each time the event occurs. The callback function is described in section Callback.

### Off

Unsubscribe from an event.

Syntax:

    DataSet.off(event, callback)

Where `event` and `callback` correspond with the parameters used to subscribe to the event.

### Events

The following events are available for subscription:

Event | Description
--- | ---
add | The `add` event is triggered when an item or a set of items is added, or when an item is updated while not yet existing.
update | The `update` event is triggered when an existing item or a set of existing items is updated.
remove | The `remove` event is triggered when an item or a set of items is removed.
* | The `*` event is triggered when any of the events `add`, `update`, and `remove` occurs.

### Callback

The callback functions of subscribers are called with the following parameters:

    function (event, properties, senderId) {
      // handle the event
    });

where the parameters are defined as

Parameter | Type | Description
--- | --- | ---
event | String | Any of the available events: `add`, `update`, or `remove`.
properties | Object | null | Optional properties providing more information on the event. In case of the events `add`, `update`, and `remove`, `properties` is always an object containing a property `items`, which contains an array with the ids of the affected items. The `update` event has an extra field `oldData` containing the original data of the updated items, and a field `data` containing the changes: the properties of the items that are being updated.
senderId | String | Number | An senderId, optionally provided by the application code which triggered the event. If senderId is not provided, the argument will be `null`.

## Data Manipulation

The data in a DataSet can be manipulated using the methods `add`, `update`, and `remove`. The DataSet can be emptied using the method `clear`.

    // create a DataSet
    var data = new vis.DataSet();

    // add items
    data.add([
      {id: 1, text: 'item 1'},
      {id: 2, text: 'item 2'},
      {id: 3, text: 'item 3'}
    ]);

    // update an item
    data.update({id: 2, text: 'item 2 (updated)'});

    // remove an item
    data.remove(3);

### Add

Add a data item or an array with items.

Syntax:

    var addedIds = DataSet.add(data [, senderId])

The argument `data` can contain:

- An `Object` containing a single item to be added. The item must contain an id.
- An `Array` containing a list with items to be added. Each item must contain an id.

After the items are added to the DataSet, the DataSet will trigger an event `add`. When a `senderId` is provided, this id will be passed with the triggered event to all subscribers.

The method will throw an Error when an item with the same id as any of the added items already exists.

### Update

Update a data item or an array with items.

Syntax:

    var updatedIds = DataSet.update(data [, senderId])

The argument `data` can contain:

- An `Object` containing a single item to be updated. The item must contain an id.
- An `Array` containing a list with items to be updated. Each item must contain an id.

The provided properties will be merged in the existing item. When an item does not exist, it will be created.

After the items are updated, the DataSet will trigger an event `add` for the added items, and an event `update`. When a `senderId` is provided, this id will be passed with the triggered event to all subscribers.

### Remove

Remove a data item or an array with items.

Syntax:

    var removedIds = DataSet.remove(id [, senderId])

The argument `id` can be:

- A `Number` or `String` containing the id of a single item to be removed.
- An `Object` containing the item to be deleted. The item will be deleted by its id.
- An Array containing ids or items to be removed.

The method ignores removal of non-existing items, and returns an array containing the ids of the items which are actually removed from the DataSet.

After the items are removed, the DataSet will trigger an event `remove` for the removed items. When a `senderId` is provided, this id will be passed with the triggered event to all subscribers.

### Clear

Clear the complete DataSet.

Syntax:

    var removedIds = DataSet.clear([senderId])

After the items are removed, the DataSet will trigger an event `remove` for all removed items. When a `senderId` is provided, this id will be passed with the triggered event to all subscribers.

## Data Selection

The DataSet contains functionality to format, filter, and sort data retrieved via the methods `get`, `getIds`, `forEach`, and `map`. These methods have the following syntax:

    DataSet.get([id] [, options]);
    DataSet.getIds([options]);
    DataSet.forEach(callback [, options]);
    DataSet.map(callback [, options]);

Where `options` is an Object which can have the following properties:

Name | Type | Required | Description
--- | --- | --- | ---
fields | String[ ] | Object.<String, String> | no | An array with field names, or an object with current field name and new field name that the field is returned as. By default, all properties of the items are emitted. When `fields` is defined, only the properties whose name is specified in `fields` will be included in the returned items.
type | Object.<String, String> | no | An object containing field names as key, and data types as value. By default, the type of the properties of an item are left unchanged. When a field type is specified, this field in the items will be converted to the specified type. This can be used for example to convert ISO strings containing a date to a JavaScript Date object, or convert strings to numbers or vice versa. The available data types are listed in section Data Types.
filter | Function | no | Items can be filtered on specific properties by providing a filter function. A filter function is executed for each of the items in the DataSet, and is called with the item as parameter. The function must return a boolean. All items for which the filter function returns true will be emitted. See section Data Filtering.
order | String | Function | no | Order the items by a field name or custom sort function.
returnType | String | no | Determine the type of output of the get function. Allowed values are `'Array' | 'Object'`. The default returnType is an Array. The Object type will return a JSON object with the ID's as keys.

The following example demonstrates formatting properties and filtering properties from items.

    // create a DataSet
    var data = new vis.DataSet();
    data.add([
      {id: 1, text: 'item 1', date: '2013-06-20', group: 1, first: true},
      {id: 2, text: 'item 2', date: '2013-06-23', group: 2},
      {id: 3, text: 'item 3', date: '2013-06-25', group: 2},
      {id: 4, text: 'item 4'}
    ]);

    // retrieve formatted items
    var items = data.get({
      fields: ['id', 'date', 'group'],    // output the specified fields only
      type: {
        date: 'Date',                   // convert the date fields to Date objects
        group: 'String'                 // convert the group fields to Strings
      }
    });

### Getting Data

Data can be retrieved from the DataSet using the method `get`. This method can return a single item or a list with items.

A single item can be retrieved by its id:

    var item1 = dataset.get(1);

A selection of items can be retrieved by providing an array with ids:

    var items = dataset.get([1, 3, 4]); // retrieve items 1, 3, and 4

All items can be retrieved by simply calling `get` without specifying an id:

    var items = dataset.get();          // retrieve all items

### Data Filtering

Items can be filtered on specific properties by providing a filter function. A filter function is executed for each of the items in the DataSet, and is called with the item as parameter. The function must return a boolean. All items for which the filter function returns true will be emitted.

    // retrieve all items having a property group with value 2
    var group2 = dataset.get({
      filter: function (item) {
        return (item.group == 2);
      }
    });

    // retrieve all items having a property balance with a value above zero
    var positiveBalance = dataset.get({
      filter: function (item) {
        return (item.balance > 0);
      }
    });

### Data Types

DataSet supports the following data types:

Name | Description | Examples
--- | --- | ---
Boolean | A JavaScript Boolean | `true` `false`
Number | A JavaScript Number | `32` `2.4`
String | A JavaScript String | `"hello world"` `"2013-06-28"`
Date | A JavaScript Date object | `new Date()` `new Date(2013, 5, 28)` `new Date(1372370400000)`
Moment | A Moment object, created with moment.js | `moment()` `moment('2013-06-28')`
ISODate | A string containing an ISO Date | `new Date().toISOString()` `"2013-06-27T22:00:00.000Z"`
ASPDate | A string containing an ASP Date | `"/Date(1372370400000)/"` `"/Date(1198908717056-0700)/"`