Sorting a Javascript object by value

Question

In my Javascript application I have an Object and I need to be able to order the array by a value within the Inner Object.

For example:

{ a : { timestamp: xxxxxx other : yyyyyy }, b : { timestamp: xxxxxx other : yyyyyy }, c : { timestamp: xxxxxx other : yyyyyy } }

What I need to do is manage this data set and re-order the array according to the timestamp of each inner object.

What ways are they that I can do to do this?

update:

My initial thought would be doing something like so:

{ a : {}, b : {}, c : {}, _ : [ c, a, b //Key's Only ] }

Then re-indexing the the object based on those values, that would sort out how to index the object, but when I insert a new element i would also have to regenerate the _ index relationship which seems way to much effort.

jfriend00 · Accepted Answer · 2011-09-14 02:31:00Z

You can copy the data to an array and then sort it:

var data = { a : { timestamp: 11111, other : "xxx" }, b : { timestamp: 22222, other : "yyy" }, c : { timestamp: 33333, other : "zzz" } }; var output = []; // copy items to an array so they can be sorted for (var key in data) { data[key].key = key; // save key so you can access it from the array (will modify original data) output.push(data[key]); } output.sort(function(a,b) { return(a.timestamp - b.timestamp); });

Generates this as output (note I added the original key to the object so it's accessible from the array):

[{"timestamp":11111,"other":"xxx","key":"a"}, {"timestamp":22222,"other":"yyy","key":"b"}, {"timestamp":33333,"other":"zzz","key":"c"}]

You can see this working here: http://jsfiddle.net/jfriend00/hXpkP/

Don't forget a hasOwnProperty test for object properties or you may include inhertied properties.

Joseph Silber · Accepted Answer · 2011-09-14 00:50:51Z

Javascript objects are not associative arrays. They may behave similarly, but they are not the same. Javascript has no associative arrays.

While associative arrays have a concept of order, Javascript objects simply do not share this particular feature with them. Objects, by there very nature, are not ordered.

So, to answer your question: you cannot order them...

Sure, objects don't have order, but that doesn't mean there isn't a possible solution.
you can create an index , hashtable of key values and "order", and when needed use the reference from one array to the object

jondavidjohn · Accepted Answer · 2011-09-14 00:58:33Z

you are not dealing with an array, but an object with property values of a, b, and c

there is no reason you would need them in a specific order, as you can't really loop over them in any particular order.

this would be trivial (using sort) if you were working with an array...

var array = [ { timestamp: xxxxxx other : yyyyyy }, { timestamp: xxxxxx other : yyyyyy }, { timestamp: xxxxxx other : yyyyyy } ]; array.sort(function(a,b) { return a.timestamp - b.timestamp; });

The problems with arrays is that they do not have string based indexes, and to have fast access to elements in need string based indexes.
all javascript indexes are strings and javascript arrays are objects, they just have a few extra useful features... one you are specifically after... jsfiddle.net/Mb8xC

Marshall · Accepted Answer · 2011-09-14 01:09:43Z

As the others have already said, you are dealing with an associative object. Not an array. Objects don't have order.

If you wish to keep it as-is, and sort an array of the keys instead, you can do this:

var obj = { a : { timestamp: xxxxxx other : yyyyyy }, b : { timestamp: xxxxxx other : yyyyyy }, c : { timestamp: xxxxxx other : yyyyyy } }; var keys = []; for(var key in obj) { keys.push(key); } keys.sort(function(a, b) { return obj[a].timestamp - obj[b].timestamp; });

Now you can access the object via the array values (e.g. obj[keys[0]], obj[keys[1]], etc). This assumes timestamps are numeric. If they are date objects the sort should be:

keys.sort(function(a, b) { return +obj[a].timestamp - (+obj[b].timestamp); });

If the timestamps are actually strings representing a date time (like 'August 2, 2012'), then it should be:

keys.sort(function(a, b) { return +new Date(obj[a].timestamp) - (+new Date(obj[b].timestamp)); });

So use whatever makes most sense in your scenario.

Community · Accepted Answer · 2017-05-23 12:29:48Z

0

You could create a custom comparer function and use the built-in sort function for arrays. See this post.

edited May 23, 2017 at 12:29

CommunityBot

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answered Sep 14, 2011 at 1:22

Annie Lagang

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