[RESOLVED] Better way to find and replace a number

[wbport]

When I find a record such as this in a textarea:

|MPC|Controller:tempo|Style:Linear Sweep|TimeRes:Quarter|SweepRes:1|Pt1:0,20|Pt2:20,28|Pt3:7,40|Pt4:33,56|Pos:8|Wide:Y

I would like to multiply the 2nd number after a Ptn: field by tfactor (already calculated) and replace it. Thus far I have

	if ((lines[i].search("|MPC|Controller:tempo") == -1))
	  continue;
	result = lines[i].match(/Pt1:\d+,(\d+)/);  
	if (result != null) {
	  old_tempo = result[1];
	  new_tempo = Math.round(old_tempo * tfactor);
	  lines[i] = lines[i].replace(old_tempo,new_tempo);	}
    else
      continue;	
	result = lines[i].match(/Pt2:\d+,(\d+)/);  
	if (result != null) {
	  old_tempo = result[1];
	  new_tempo = Math.round(old_tempo * tfactor);
	  lines[i] = lines[i].replace(old_tempo,new_tempo); }
    else
      continue;	//...... similar code for 3 & 4 follows

There will be from 1 to 4 Pts, if one is missing there will not be a next one.

My problem is I replace the first occurrence of any number I find and for certain factors (2 in this case) it could change an already converted number and leave other fields in the record alone. I could split the line on commas to change the first number I find but can't be certain if there are no other commas elsewhere on the line.

TIA

P.S The page is tchange.htm.

[clueful]

<script type='text/javascript'>

str = 
"|MPC|Controller:tempo|Style:Linear Sweep|TimeRes:Quarter|SweepRes:1|Pt1:0,20|Pt2:20,28|Pt3:7,40|Pt4:33,56|Pos:8|Wide:Y";

function change( str, tfactor )
{
 var rxp, idx = 1, data, startFrom, foundAt;
 
 while( data = ( rxp = new RegExp( "(Pt)(" + (idx++) + ")(:\\d+,)(\\d+)",'g') ).exec( str ) )
 {
  foundAt = data.index;
  startFrom = rxp.lastIndex;  
  str = str.substring( 0, foundAt ) + data[ 1 ] + data[ 2 ] + data[ 3 ] + ( Number( data[ 4 ] ) * tfactor ) + str.substring( startFrom );
 }
 
 return str;   
}

document.write( str + '<br>===========================<br>');

document.write( change(str, 2) ); /* Multiply by 2 */

</script>

[wbport]

Many thanks! Just what I needed. I knew it needed something involving regular expressions and making a substitution at only specific places, but i didn't know where to begin except for an awkward workaround.

I credit you on the final version (link on 1st message).