#!/usr/bin/perl

use strict;
use Data::Dumper;

my @harray = (
          "Size",
          "Buffer Size",
          "Value",
          "Size",
          "Buffer Size",
          "Value",
          "Size",
          "Buffer Size",
          "Value"
        );

my @OneHead = ("Size",
               "Buffer Size"
        );

my %seen = map { $_ => 0 } @OneHead;
my @results = grep {
    /(\w+)/;
    my $s = $1;
    !exists $seen{$s} or ($seen{$s}++ < 1);
} @harray;

local $" = $/;
print "@results\n";

OUTPUT:
------

@result = ("Size", "Buffer Size", "Value", "Value", "value");