x y z
a b c
e f g
h i j

##</code><code>##

x y z
# a b c <- inserted element in position 0 
e f g
h i j

##</code><code>##

for my $rc(@R) {
        if ($rc->[0] eq "a") {
                splice @R, 0, 0, '#';
                print "$rc->[0]\t","$rc-[1]\t","$rc->[2]\t","$rc->[3]\n"
        }
}

##</code><code>##

x y z
a b c
a b c
a b c
a b c
.
.