knockout-arraytransforms 

Allows for creating efficient transformations of observable arrays.

``JavaScript
var integers = ko.observableArray([
ko.observable(10), ko.observable(9),
ko.observable(8), ko.observable(7),
ko.observable(6), ko.observable(5),
ko.observable(4), ko.observable(3),
ko.observable(2), ko.observable(1)
]);

var evenIntegersOver5 =
integers.sortBy(function (n) {
return n();
}).filter(function (n) {
n = n();
return n > 5 && n % 2 === 0;
});

// ko.toJS(evenIntegersOver5) -> [6, 8, 10];

// The sortBy and filter callbacks are only called for these new items, not
// every item in the array.
integers.splice(0, 0, ko.observable(12), ko.observable(11));

// ko.toJS(evenIntegersOver5) -> [6, 8, 10, 12];

// Set the observable containing 1 in the original array to 14. Again, the
// sortBy and filter callbacks are only called once on index 11. sortBy has
// all of the previous sort keys cached and performs a fast binary sort.
integers()11;

// ko.toJS(evenIntegersOver5) -> [6, 8, 10, 12, 14];
`

Transformations

all/every, any/some, filter/reject, groupBy, map, sortBy.

Callback functions receive two arguments: an item in the original array, and an observable containing the index of that item in the original array.

`JavaScript
var animals = ko.observableArray(["cat", "dog"]);

var ranks = animals.map(function (name, index) {
return name + ": " + (index() + 1);
});

// ranks() -> ["cat: 1", "dog: 2"];

animals.reverse();

// ranks() -> ["dog: 1", "cat: 2"];
`

`groupBy` returns an array of objects containing a key string and a values observableArray.

`JavaScript
var integers = ko.observableArray([1, 2, 3, 4, 5]);

var evenOrOdd = integers.groupBy(function (n) {
// return value is always coerced into a string
return n % 2 === 0;
});

// evenOrOdd() -> [
// { key: "false", values: ko.observableArray([1, 3, 5]) },
// { key: "true", values: ko.observableArray([2, 4]) }
// ]
`

Create your own

For examples, see `ko.arraytransforms.createTransform`` in the source code.

License

X11. See LICENSE.