if(!exists $result{$uniqueKey}) # If this combinaison is unknown
   {
     $result{$uniqueKey} = [\%currentRow]; # save the current row to i
+t
   }
   else
   {
     push @{ $result{$uniqueKey} }, \%currentRow; # add the current ro
+w to the existing ones
   }
[download]

The exists test is not needed because autovivification (see perlglossary) will create an empty anonymous array reference to push a new value into in the case of a key that does not already exist:

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump;
 ;;
 my @ra = qw(foo a  bar w  bar x  foo b  bar y);
 dd \@ra;
 ;;
 my %hash;
 while (@ra >= 2) {
   my $k = shift @ra;
   my $v = shift @ra;
   ;;
   push @{ $hash{$k} }, $v
   }
 dd \%hash;
 ;;
 @ra = qw(foo A  bar W  bar X  foo B  bar Y);
 dd \@ra;
 ;;
 my $hashref;
 while (@ra >= 2) {
   my ($k, $v) = splice @ra, 0, 2;
   push @{ $hashref->{$k} }, $v;
   }
 dd $hashref;
"
["foo", "a", "bar", "w", "bar", "x", "foo", "b", "bar", "y"]

{ bar => ["w", "x", "y"], foo => ["a", "b"] }

["foo", "A", "bar", "W", "bar", "X", "foo", "B", "bar", "Y"]

{ bar => ["W", "X", "Y"], foo => ["A", "B"] }
[download]