noticeable delay in processing a loop

[Fabian]

I have the following lopp inside one of my scripts

document.getEle mentById('text' ).innerHTML = "";
for (i = 0; i < txtdef.length; i++) {
if (xx == txtdef[i][0]) {
if (yy == txtdef[i][1]) {
if (level == txtdef[i][2]) {
document.getEle mentById('text' ).innerHTML = "<P>" + txtdef[i][3] +
"</P>";
}
}
}
}

txtdef is an array. In this case, it only has about 4 rows, but there is
no theoretical limit. However, there is a noticeable delay in processing
when this sequence is triggered. I was wondering if there is a more
efficient way of writing this routine?


--
--
Fabian
Visit my website often and for long periods!

http://www.lajzar.co.uk

[Fabian]

Re: noticeable delay in processing a loop

Fabian hu kiteb:
[color=blue]
> I have the following lopp inside one of my scripts[/color]
[color=blue]
> txtdef is an array. In this case, it only has about 4 rows, but there
> is no theoretical limit. However, there is a noticeable delay in
> processing when this sequence is triggered. I was wondering if there
> is a more efficient way of writing this routine?[/color]

I found the principal answer. writing that text was causing the document
to reflow, and it was the reflowing that caused the slowdown. Judicious
use of div has now removed that cause of delay.


--
--
Fabian
Visit my website often and for long periods!

http://www.lajzar.co.uk

[Dr John Stockton]

Re: noticeable delay in processing a loop

JRS: In article <bqseqj$256tov$ 1@ID-174912.news.uni-berlin.de>, seen in
news:comp.lang. javascript, Fabian <lajzar@hotmail .com> posted at Sat, 6
Dec 2003 20:37:12 :-[color=blue]
>I have the following lopp inside one of my scripts
>
> document.getEle mentById('text' ).innerHTML = "";
> for (i = 0; i < txtdef.length; i++) {
> if (xx == txtdef[i][0]) {
> if (yy == txtdef[i][1]) {
> if (level == txtdef[i][2]) {
> document.getEle mentById('text' ).innerHTML = "<P>" + txtdef[i][3] +
>"</P>";
> }
> }
> }
> }[/color]

document.getEle mentById('text' ).innerHTML = "";
for (i = 0; i < txtdef.length; i++) {
T = txtdef[i]
if (xx == T[0]) {
if (yy == T[1]) {
if (level == T[2]) {
document.getEle mentById('text' ).innerHTML = "<P>" + T[3] + "</P>";
}
}
}
}


should make a small difference, and is a good idea anyway.

document.getEle mentById('text' ).innerHTML = "";
for (i = 0; i < txtdef.length; i++) {
T = txtdef[i]
if ( xx == T[0] && yy == T[1] && level == T[2] ) {
document.getEle mentById('text' ).innerHTML = "<P>" + T[3] + "</P>";
}
}

is IIRC equivalent, and could be a bit quicker.

But I've seen your second post in this thread.

document.getEle mentById('text' ).innerHTML = "";
for (i = 0; i < txtdef.length; T = txtdef[i++])
if ( xx == T[0] && yy == T[1] && level == T[2] )
document.getEle mentById('text' ).innerHTML = "<P>" + T[3] + "</P>";

For a further improvement, note that only the last assignment has
effect.

document.getEle mentById('text' ).innerHTML = "";
for (i = txtdef.length; i >=0 ; T = txtdef[--i])
if ( xx == T[0] && yy == T[1] && level == T[2] ) {
document.getEle mentById('text' ).innerHTML = "<P>" + T[3] + "</P>" ;
break }

S = "" ;
for (i = txtdef.length; i > 0 ; T = txtdef[--i])
if ( xx == T[0] && yy == T[1] && level == T[2] ) {
S = "<P>" + T[3] + "</P>" ;
break }
document.getEle mentById('text' ).innerHTML = S ;



All untested.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://jibbering.com/faq/> Jim Ley's FAQ for news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> JS maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/JS/&c., FAQ topics, links.

[Fabian]

Re: noticeable delay in processing a loop

Dr John Stockton hu kiteb:
[color=blue]
> document.getEle mentById('text' ).innerHTML = "";
> for (i = 0; i < txtdef.length; i++) {
> T = txtdef[i]
> if ( xx == T[0] && yy == T[1] && level == T[2] ) {[/color]

Testing all these if statements at the same time is faster than testing
them in series? I would be very interested in a definitive answer to
this one.
[color=blue]
> S = "" ;
> for (i = txtdef.length; i > 0 ; T = txtdef[--i])
> if ( xx == T[0] && yy == T[1] && level == T[2] ) {
> S = "<P>" + T[3] + "</P>" ;
> break }
> document.getEle mentById('text' ).innerHTML = S ;
>
>
>
> All untested.[/color]

Tested, and working quite happily. Thank you. Improvements are slight
compared to when I removed the text reflow situation, but still useful.
The overall javascript throws around so many images that any little
speed increase is useful.


--
--
Fabian
Visit my website often and for long periods!

http://www.lajzar.co.uk

[Dr John Stockton]

Re: noticeable delay in processing a loop

JRS: In article <bqvais$25pgq4$ 1@ID-174912.news.uni-berlin.de>, seen in
news:comp.lang. javascript, Fabian <lajzar@hotmail .com> posted at Sun, 7
Dec 2003 22:43:28 :-[color=blue]
>Dr John Stockton hu kiteb:
>[color=green]
>> document.getEle mentById('text' ).innerHTML = "";
>> for (i = 0; i < txtdef.length; i++) {
>> T = txtdef[i]
>> if ( xx == T[0] && yy == T[1] && level == T[2] ) {[/color]
>
>Testing all these if statements at the same time is faster than testing
>them in series? I would be very interested in a definitive answer to
>this one.[/color]

In each case, the testing can stop once the result is known. In a
compiled language that permits partial boolean evaluation, the above
approach should certainly be quicker. In javascript, it might or might
not be. Certainly, if xx!=T[0] there is no need to test further &&
items.

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://jibbering.com/faq/> Jim Ley's FAQ for news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> JS maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/JS/&c., FAQ topics, links.