There is definitely no need for all of those splits. If you want an array that contains all numbers, e.g. you want to replace a single array element "(0,670)" with two array elements one for each number. You could do the following:

use strict;
use warnings;

while (my $line = <DATA>) {

  #remove all whitespace
  $line =~ s/\s//g;

  #split line
  my @aFields = split(/;/, $line);

  #remove parenthesised field
  my $sFld1 = shift @aFields;

  #convert parenthesized field to numbers
  my ($sNoParens) = ($sFld1 =~ /^\(([^)]*)\)$/);
  my @aSubFields = split(/,/, $sNoParens);

  # if you want to make sure there are only N
  # numbers, do your checks here.

  #put the numbers where fld0 was originally
  unshift @aFields, @aSubFields;

  #print the result
  print "<@aFields>\n";
}

__DATA__
( 0, 670); 3.2; 7.8; 9.4; 10.2; 12.6;
[download]

See shift and unshift for more information.

Best, beth