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Message-ID: <8931625.SEqChMirdb@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
Organization: PointedEars Software (PES)
Date: Thu, 03 Nov 2011 20:41:25 +0100
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Subject: Re: sorting columns
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Andreas Bergmaier wrote:

> Dr J R Stockton schrieb:
>> Why sort a<table>?
> Why not?

Because that is comparably inefficient.

>> Supply the data in JavaScript, as a "two-dimensional array"
>>    Arr[[..., ..., ...   ], [...], [...], [...], ... [...]] ;
>>
>> At need, sort that.  Then remove any existing Table, build the new Table
>> using DOM methods, and insert the new Table.
> 
> What do you mean with two-dimensional array?

There are no multi-dimensional arrays in ECMAScript implementations, only 
arrays, represented by Array instances, that can contain references to other 
Array instances as elements.

> Does it represent the cell data, or does each second-level-array contain
> the relevant cell content (of the column you want to sort) and a reference
> to the row element?

Yes.

> I guess it would be faster to store the dom elements, instead of
> rebuilding them.

If you mean references to DOM element objects, that is an interesting idea.  
The main problem with sorting the table in-situ is that this implicitly 
requires a considerable number of modifications of the node-relative 
structure.

However, you should take into account the time it takes to access a property 
of a host object, that is referred to by a property of an Array instance, 
that yields a primitive, but computed, value, compared to accessing a 
property of an Array instance that stores a primitive value (the length of 
the first part of that sentence compared to the length of the second one 
should make you think already).

> A littlebit faster might be something like
>     r = [], tr = table.rows;
>     for (var i=1; i<tr.length; i++)
>        r.push( [tr[i].cells[column].textContent, row] ); // slice and map
>     r.sort(function(a, b) {
>         return mysortfunction(a[0], b[0]);
>     });
>     for (var i=0; i<length; i++)
>        table.insertRow(r[i][1]);
> 
> Disclaimer: I'm not sure about standard-compliancy of all browsers
> regarding * <table>.rows
> * <table>.insertRow(<tr>)
> * <tr>.cells
> * <*>.textContent
> * Array.prototype.sort(fn)

Support for the `rows' and `cells' properties, and Array.prototype.sort()  
should be ubiquitous by now [1,2].  The `textContent' property, on the other 
hand, requires an implementation of the Node interface of W3C DOM Level 3 
Core, which e. g. MSHTML before version 9 does not provide [3].


PointedEars
___________
[1] <http://www.w3.org/TR/1998/REC-DOM-Level-1-19981001/level-one-html.html>
    <http://msdn.microsoft.com/en-us/library/ms537484(VS.85).aspx>
[2] <http://pointedears.de/scripts/test/es-matrix/#a>
[3] <https://developer.mozilla.org/En/DOM/Node.textContent>
    <http://msdn.microsoft.com/en-us/library/ff974773(VS.85).aspx>
-- 
Anyone who slaps a 'this page is best viewed with Browser X' label on
a Web page appears to be yearning for the bad old days, before the Web,
when you had very little chance of reading a document written on another
computer, another word processor, or another network. -- Tim Berners-Lee