An indexed record Datasaur module.

The datasaur-indexed data source provides a means to map the original set of rows, resulting in a subset of particular rows in a particular order.

Instantiation

datasaur-indexed sits on top of a static datasource. For example:

var Source = require('datasaur-local'); // v3.0.0 or higher
var Indexer = require('datasaur-indexed'); // this version must be >= that of datasaur-local
var dataModel = new Indexer(new Source);

Custom Properties

datasaur-indexed introduces a custom index property and some helper methods described in the next section.

index

The index property, when defined, is an integer array that maps the y value (row index provided to other method calls) to specific rows in the original set of rows. This property is all that is needed to effectively "index" (reorder, filter, and/or alias) the data.

Given the following set of rows (shown here in JSON syntax):

[
  { "name": "Sam", "gender": "M" },
  { "name": "Al", "gender": "F" },
  { "name": "Max", "gender": "M" },
  { "name": "Jo", "gender": "F" }
]

To filter the data:

dataModel.index = [0, 2] // rows where second column is 'M'

To order the data:

dataModel.index = [1, 3, 2, 0] // alpha ascending by first column

To alias all rows:

dataModel.index = [0, 0, 1, 1, 2, 2, 3, 3]

To remove the index and revert to the original set of rows:

dataModel.index = undefined
``

While the above approach works, it is wholly inadequate, however, as a generalized solution for filtering and sorting.
See [`buildIndex`](#dataModel-buildIndex-predicate) and [_Generalized sorting_](#generalized-sorting) below for better solutions.

### Custom methods
#### `dataModel.setIndex(index)` _(instance method)_
Using the `dataModel.setIndex([...])` method, rather than assigning directly to `dataModel.index`, will dispatch the pre- and post-index data events back to the applicaiton (see [_Event strings_](#event-strings) below).
`dataModel.buildIndex` and `dataModel.sort` both call `dataModel.setIndex`.
Calling without an argument is the same as calling `dataModel.clearIndex`.

#### `dataModel.clearIndex()` _(instance method)_
Undefines the `index` (by calling `setIndex(undefined)`).

#### `dataModel.buildIndex(predicate)` _(instance method)_

Builds a new index and calls `dataModel.setIndex` on it:
```js
dataModel.buildIndex(predicate);

where predicate returns truthy for desired rows, for example:

function predicate(y) {
    return this.getValue(1, y) === 'M'; // rows where second column is 'M'
}

Calling without a predicate is the same as calling dataModel.clearIndex().

DatasaurIndexed.valOrFunc (static method)

Note that the above example predicate would fail on a computed cell or column. To properly handle such data, you can use DatasaurIndexed.valOrFunc instead of calling this.getValue:

function predicate(y) {
    return DatasaurIndexed.valOrFunc(this.getRow(y), 'gender', this.schema.gender.calculator)  === 'M'; // rows where second column is 'M'
}

Event strings

The event string definitions have the following defaults:

DatasaurIndexed.preindexEventString = 'fin-hypergrid-data-prereindex';
DatasaurIndexed.postindexEventString = 'fin-hypergrid-data-postreindex';

Generalized sorting

For generalized single-column sorting, use datasaur-simple-sort, which sits on top of datasaur-indexed:

var Sorter = require('datasaur-simple-sort');
var dataModel = new Sorter(new Indexer(new Source));
dataModel.sort(0); // alpha ascending by first column

As noted in datasaur-simple-sort's README, it fails on computed cells and columns.

Sorting by multiple columns, each of which may be ascending or descending, is somewhat more complicated, essentially involving dynamically adding a Sorter stage for each column to be sorted. See datasaur-filter which does something like that, but forces Array.prototype.sort to do a stable sort (which is is not naturally inclined to do), and properly handles computed cells and columns. Note: As of this writing datasaur-filter has not yet been updated to v3.0.0.