Computed array sorting

Question

I have a computed array like this,

self.weapons = ko.observableArray(
  []
  );

self.wings = ko.observableArray(
  []
  );


 self.itemList = ko.computed( function()
 {
     return self.weapons().concat(self.wings());
 }
 },
 this );

i would like to sort this array.

i can sort ko.observableArray with no problem.

issue here is i think, ko.computed is computes back again after the sorting is done.

also: is there a better way concatenating multiple observableArrays together?

Thank you.

Jeff Mercado · Accepted Answer · 2015-04-28 03:50:40Z

2

Just sort the concatenated array.

self.itemList = ko.computed(function () {
    var weapons = self.weapons(),
        wings = self.wings();
    return weapons.concat(wings).sort();
});

It will have to be resorted every time either array changes but there's not much you can do about that.

If you are going to make many changes in succession, consider using the rateLimit extender (or throttle prior to knockout 3.1.x) on your computed observable. This will limit the amount of times notifications are sent out by the observable by collapsing all notifications made within a certain time period.

self.itemList = ko.computed(function () {
    ...
}).extend({ rateLimit: 500 }); // wait at least 500ms before first notification

edited Apr 28, 2015 at 3:50

answered Sep 18, 2012 at 5:57

Jeff Mercado

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8 Comments

mikbal Over a year ago

thank you. this works of course, but it is extremely slow. adding 100 items essentially means 100^2*log100. ideally concatenation would be shallow, and sort only needed when list is complete. forget the shallow merge, is it possible to sort this array only when i want it. like after adding 100 elements, instead of every push.

Jeff Mercado Over a year ago

Will you be modifying the arrays in quick succession or will it change over long periods of time? Would you rather have it throttled sorting (so you can add many quickly but will sort after it stops changing for a while) or do you want it sorted on demand? I'm sure that would be possible to write up, I'll just need to know what your goal is for it.

mikbal Over a year ago

just want suppress sorting when i add many items in succession.

Jeff Mercado Over a year ago

In that case, you can throttle your arrays so it doesn't get updated too frequently.

mikbal Over a year ago

it was that easy huh. i reduced iteration count from 100 to 1. brilliant! thank you

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