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Is there a way to map a value in an object to the index of an array in javascript?

Prepending that a solution only needs to work in the latest versions of Chrome, Firefox, and Safari as a bonus.
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I am trying to use an associative array for a large data set with knockout. My first try made it a true associative array:
[1: {Object}, 3: {Object},...,n:{Object}]
but knockout was not happy with looping over that. So I tried a cheating way, hoping that:
[undefined, {Object}, undefined, {Object},...,{Object}]
where the location in the array is the PK ID from the database table. This array is about 3.2k items large, and would be iterated over around every 10 seconds, hence the need for speed. I tried doing this with a splice, e.g.
$.each(data, function (index, item) {
self.myArray.splice(item.PKID, 0, new Object(item));
}
but splice does not create indices, so since my first PKID is 1, it is still inserted at myArray[0] regardless. If my first PK was 500, it would start at 0 still.
My second thought is to initialize the array with var myArray = new Array(maxSize) but that seems heavy handed. I would love to be able to use some sort of map function to do this, but I'm not really sure how to make the key value translate into an index value in javascript.
My third thought was to keep two arrays, one for easy look up and the other to store the actual values. So it combines the first two solutions, almost, by finding the index of the object in the first example and doing a lookup with that in the second example. This seems to be how many people manage associative arrays in knockout, but with the array size and the fact that it's a live updating app with a growing data set seems memory intensive and not easily manageable when new information is added.
Also, maybe I'm hitting the mark wrong here? We're putting these into the DOM via knockout and managing with a library called isotope, and as I mentioned it updates about every 10 seconds. That's why I need the fast look up but knockout doesn't want to play with my hash table attempts.
--
clarity edits:
so on initial load the whole array is loaded up (which is where the new Array(maxLength) would go, then every 10 seconds anything that has changed is loaded back. That is the information I'm trying to quickly update.
--
knockout code:
<!-- ko foreach: {data: myArray(), afterRender: setInitialTileColor } -->
<div class="tile" data-bind="attr: {id: 'tileID' + $data.PKID()}">
<div class="content">
</div>
</div>
<!-- /ko -->
Then on updates the hope is:
$.each(data.Updated, function (index, item) {
var obj = myModel.myArray()[item.PKID];
//do updates here - need to check what kind of change, how long it's been since a change, etc
}

Here is a solution how to populate array items with correct indexes, so it doesn't start from the first one (0 (zero) I meant)
just use in loop
arr[obj.PKID] = obj;
and if your framework is smart (to use forEach but not for) it will start from your index (like 500 in case below)
http://jsfiddle.net/0axo9Lgp/
var data = [], new_data = [];
// Generate sample array of objects with index field
for (var i = 500; i < 3700; i++) {
data.push({
PKID: i,
value: '1'
});
}
data.forEach(function(item) {
new_data[item.PKID] = item;
});
console.log(new_data);
console.log(new_data.length); // 3700 but real length is 3200 other items are undefined

It's not an easy problem to solve. I'm assuming you've tried (or can't try) the obvious stuff like reducing the number of items per page and possibly using a different framework like React or Mithril.
There are a couple of basic optimizations I can suggest.
Don't use the framework's each. It's either slower than or same as the native Array method forEach, either way it's slower than a basic for loop.
Don't loop over the array over and over again looking for every item whose data has been updated. When you send your response of data updates, send along an array of the PKIds of the updated item. Then, do a single loop:
.
var indexes = []
var updated = JSON.parse(response).updated; // example array of updated pkids.
for(var i=0;i<allElements.length;i++){
if(updated.indexOf(allElements[i].pkid)>-1)
indexes.push(i);
}
So, basically the above assumes you have a simple array of objects, where each object has a property called pkid that stores its ID. When you get a response, you loop over this array once, storing the indexes of all items that match a pk-id in the array of updated pk-ids.
Then you only have to loop over the indexes array and use its elements as indexes on the allElements array to apply the direct updates.

If your indexes are integers in a reasonable range, you can just use an array. It does not have to be completely populated, you can use the if binding to filter out unused entries.
Applying updates is just a matter of indexing the array.
http://jsfiddle.net/0axo9Lgp/2/

You may want to consider using the publish-subscribe pattern. Have each item subscribe to its unique ID. When an item needs updating it will get the event and update itself. This library may be helpful for this. It doesn't depend upon browser events, just arrays so it should be fairly fast.

remove specific item from a json object

i am trying to remove some items in an json object list, the ones that have a specific group. My JSON looks like this.
var events = [
{"id":"19","name":"sports","group":"1"},
{"id":"20","name":"school","group":"2"},
{"id":"21","name":"fun","group":"1"}
]
I tried this
for(var i in events)
if(events[i].group == deleted_group)
events.splice(i, 1);
But the problem of this, is that if i have to remove more items, it bugs out. Is there another easy way to to this ? I am open for sugestion even using underscore.js .
Thank you in advance, Daniel!

Try this
var events = [
{"id":"19","name":"sports","group":"1"},
{"id":"20","name":"school","group":"2"},
{"id":"21","name":"fun","group":"1"}
]
console.log(_.reject(events, function(event){ return event.group == '1'; }));

When you're using the "splice" function to remove elements from the array inside a for loop,
you need to shift your current index back when removing an item since the array is reindexed.
Also take a look at the array functions like "filter" for a more convenient way, read more on MDN.

You can use delete operator to delete objects (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/delete):
delete events[0]
The problem with delete is, that in your array, as a value of events[0] it will leave undefined.
So another way (the way I would choose for your simple example) is to just rewrite the array:
var temp_events = [];
for(var i in events)
if(events[i].group != deleted_group)
temp_events[temp_events.length] = events[i];
events = temp_events;
Executing splice in a for loop has complexity n^2 (where n is number of elements). Rewriting has linear complexity.

Working with Data Attributes - Build a List & See if One Exists

I have 2 questions based on the graphic below:
How can I tell if one of the 'data-conversationmessageuserid' data attributes with a specific value exists - say 1000000003? I believe data selectors is what I need and have tried the following but its not working yet:
if($('#conversationsInBoxMessagesWrapperDIV')['data-conversationmessageuserid=1000000003']) {
// do something
}
How could I get all the 'data-conversationmessageuserid' data attributes into an array and the loop through them? I'm still playing with this code but its far from publishable. Trying to use .map
.map(function()
thankyou so much

Try:
if($('#conversationsInBoxMessagesWrapperDIV [data-conversationmessageuserid=1000000003]').length)
or
$('#conversationsInBoxMessagesWrapperDIV').find('[data-conversationmessageuserid=1000000003]') //Or children only to look at one level.
To get all the data values you could do:
var conversationmessageuserids = $('#conversationsInBoxMessagesWrapperDIV').children().map(function(){
return $(this).data('conversationmessageuserid');
}).get();

jQuery supports data attributes: http://api.jquery.com/data/
So you could do if($('#conversationsInBoxMessagesWrapperDIV').data('conversationmessageuserid') === 1000000003)

Remove element from jQuery object

I have a jQuery object that is created via jQuery .find() as seen below...
var $mytable= $('#mytable');
var $myObject = $mytable.find("tbody tr");
This works great and creates a jQuery object of all the tr elements in the tbody. However, as I'm looping over the data, I need to be able to remove parts of the object as I go. For instance, if the above call returns a jQuery object named $myObject with a length of 10, and I want to remove the index 10, I thought I could just do $myObject.splice(10,1) and it would remove the element at index 10. However this doesn't seem to be working.
Any ideas why? Thank you!
UPDATE
I basically just want to be able to remove any element I want from $myObject as I loop through the data. I know it's zero based (bad example above I guess), was just trying to get my point across.
UPDATE
Okay, so I create the object using the find method on the table and at it's creation it's length is 24. As I loop over the object, when I hit an element I don't want I tried to use Array.prototype.splice.call($rows,x,1) where x represents the index to remove. Afterwards when I view the object in the console, it still has a length of 24.

Use .not() to remove a single element, then loop through the jQuery object at your leisure:
var $myObject = $mytable.find('tbody tr').not(':eq(9)'); // zero-based
http://jsfiddle.net/mblase75/tLP87/
http://api.jquery.com/not/
Or if you might be removing more than one:
var $myObject = $mytable.find("tbody tr:lt(9)");
http://jsfiddle.net/mblase75/9evT8/
http://api.jquery.com/lt-selector/

splice is not part of the jQuery API, but you can apply native Array methods on jQuery collections by applying the prototype:
Array.prototype.splice.call($myObject, 9, 1); // 0-index
You can also use pop to remove the last item:
Array.prototype.pop.call($myObject);
This should also give you a correct length property.

splice is an array method, not a jQuery object method.
Try slice

Javascript uses zero-based arrays. This means that the final item in the array (i.e. the 10th item) will be at index 9.
$myObject[9]
So you need something like this:
$myObject.splice(9, 1);
This will remove the element from your existing array, and also return it.

You could also use filter :
var $myObject = $mytable.find("tbody tr").filter(':lt(9)');

You can use .remove to remove an element from the DOM.
So to remove the element at index 9 of the $myObject array, use:
$myObject.eq(9).remove();
If you want to keep the element that you are removing, you can also do:
var removedElement = $myObject.eq(9);
removedElement.detach();

Javascript: how to get values from all selected checkboxes from a table

I've searched in many threads but i don't see any checkboxes that involves tables, i just wanted to make deleting easy for users, Say, i have a table with fifty entries and i wanted to delete 10 all in one go, so i select the check box beside each record so when i want to delete it it will just get the values of the checkbox pass it on to a php script..
My question is how do i im[plement this on Javascript or jQuery?. getting the values from n numbers of checkboxes? since tables have a dynamic value depending on how many it has on the database.
Here is an image to be clear:

This will give you an array containing the value attribute of each checked box:
var values = $('input:checked').map(function() {
return this.value;
}).get();
See http://jsfiddle.net/p58Hw/1/

Select your table, find all rows with a checked checkbox, store their values, and remove them:
var $chkboxes = $(yourTable).find("tr input[type='checkbox']:checked");
var checkBoxVals = $chkboxes.map(function(){ return $(this).val(); }).toArray();
$chkboxes.closest('tr').remove();
// serialize array checkBoxVals and pass it to your php script

You would post your code. But try something like this:
$('.YourCheckboxClass:checked').each(function() {
// your code here
});