$re = '/(?<sequenceFlag>[{,])\s*(?<key>\w+)\s*=\s*(?<value>\([^)]+\))\s*(?<terminatingFlag>\}?)/';
$str = '{xRate=(250.0, 260.0) , yValue =(1.51, 1.54)} ... { xRate = (250.0, 260.0) }
... { yValue=(1.51, 1.54) } ... { xRate = ( 250.0 , 260.0), yValue=(1.51, 1.54) }
{ xRate = ( 250.0, 260.0 ) ,yValue=(1.51,1.54), zItem =( foo, bar,baz) } ... {xRate=(250.0,260.0)}
';
$subst = "['$2', '$3'], ";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php