Rotate Cartesian coordinates.
Perl, 112 80 78
 
s/\S*//;$c=cos$&amp;;$s=sin$&amp;;s/([^ ,]*),(\S*)/($1*$c-$2*$s).&quot;,&quot;.($1*$s+$2*$c)/ge

Run on command-line as perl -pe 'code here', p option counted in code size.
For reference, here's my previous approach.  But regexes are too damn powerful.
split/[ ,]/,&lt;&gt;;$_='A;Y,print$x*cos($a)-$y*sin$a,&quot;,&quot;,$x*sin($a)+$y*cos$a,$&quot;whileX';s/[AXY]/\$\l$&amp;=shift\@_/g;eval