ansaurus

Question

How to select elements from a set that are children of another element

Answer 1

A:

I don't know about jQuery but in YUI3 nodelists returned from a selector query contain the actual selector string used to create the list, perhaps jquery exposes similar functionality?

unomi 2010-06-16 09:06:44

Thanks for the downvote. The question explicitly asked to not loop through the sets. I am not sure if it is worth making the distinction of a forEach vs filter...

unomi 2010-06-16 09:41:42

Answer 2

+2 A:

You can use the .filter method to reduce the elements to those that match a specific selector:

mySet.filter("div#foo > *");

You can also get the selector used in a jQuery object by accessing the .selector property.

Andy E 2010-06-16 09:13:07

You don't always have a selector, you might have a collection: `$('div > :hidden').add('p').filter(':odd')` - I doubt you'll get a correct selector there, though I haven't checked.

Kobi 2010-06-16 09:29:26

Just a note, filter would exactly loop through all the elements of (in this case) mySet, albeit not _manually_.

unomi 2010-06-16 09:37:56

@unomi: Very few jQuery selectors and DOM traversal methods are free of loops. The ones that don't involve loops are the ones that can attain the elements using `querySelectorAll()`, which isn't supported in older browsers. The point is that `.filter()` handles the looping *and* the condition checking for you.

Andy E 2010-06-16 10:51:59

Answer 3

+1 A:

Interesting. Assuming you have two jQuery collections and you don't know the selectors:

var myContainer = $('div');
var mySet = $('h3:even');

filter seems to work:

myContainer.children().filter(mySet)

Keep in mind, however, that this is undocumented as far as I can see, so it may change.
.not can also accept a collection of elements, which works similarly.

Working example: http://jsbin.com/owuru

Kobi 2010-06-16 09:20:05

As would this loop through myContainer.children, and compare each one to (worst case) each of mySet.

unomi 2010-06-16 09:39:30

@unomi - this is essentially intersecting two sets, so yes, you have to go through both. In terms of complexity, it could be done in `nlogn`, and this is probably `n²`. Note that I did not assume there's a single parent.

Kobi 2010-06-16 09:47:57

All I meant with my answer is that it is possible that the initial selector is actually available, as Andy E confirmed - but as you later stated it is possible that they are not necessarily 'pure' selector generated lists, it renders my suggestion moot. If performance is a concern you should likely ensure that smallset.filter(largeset) and optionally remove hits from the largeset.

unomi 2010-06-16 09:56:56

@Kobi I am not quite sure what you meant by "Note that I did not assume there's a single parent."

unomi 2010-06-16 10:00:37

Sorry, I meant that `myContainer` may have more than a single element, "parent" is the wrong word here. I also use `.children` as a helper - My answer is really about intersecting two sets, which starts one step after `.children` was called. I see it as `var set1 = $('selector1'); var set2 = $('#id').children(); var result = set2.filter(set1);`

Kobi 2010-06-16 10:05:56

Yes, I think that is a good general solution.

unomi 2010-06-16 10:12:43

Thanks, this worked fine for me and filled my criteria :) Even though this is undocumented, it seems to work in the current jQuery version which is fine by me.

Tatu Ulmanen 2010-06-16 10:38:02

ansaurus

tags:

views:

answers:

How to select elements from a set that are children of another element

related questions