$ cat tmp/tmp.pl && perl tmp/tmp.pl
#!/usr/bin/perl
#
use strict;
use warnings;
my $heading=readline(DATA);
my @headings=split/,/,$heading;
print $heading;
my (@index,@values);
while(<DATA>){
chomp;
    if (/^(\w+),\s*$/){
        push @index,$1;
    }
    else{
        @values=split/,/,$_;
    }
}
my $row = 0;
for my $record (@index){
    print join(",\t", $record, @values[(scalar(@headings) * $row) .. ((scalar(@headings) * $row) + $#headings -1)]),"\n";
    $row++;
}


__DATA__
    a,       b,    c,   d
aa,
bb,
aa,
bb,
12,33,102,111,223,24,88,56,99,130,21,45,88,90,212,500
    a,       b,    c,   d
aa,     12,     33,     102
bb,     223,    24,     88
aa,     99,     130,    21
bb,     88,     90,     212