my @input_numbers = (1, 2, 4, 8, 16, 32, 64);
my @result = map {
        my @digits = split //, $_;
        if ($digits[-1] == 4) {
            join ”,@digits;
        } else {
          (  );
        }
} @input_numbers;
print “@result”;

OUTPUT: 4 64

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配列の差集合などの取り方メモ。
http://dev-man.seesaa.net/article/117885645.html から引用。

——————

Perlは問題点の多い言語と言われますが、やはり実用性は本当に高いな、と思う今日このごろ。大きなプログラムを書いても遅くならないし。

さて、2つの配列の積集合（共通する要素）、和集合（いずれか一方または両方に含まれる要素）、差集合（一方にのみ含まれる要素）を求めるには、List::Compare が便利みたいなので試してみた。

#!/usr/bin/perl

use List::Compare;

# 比較する二つの配列
my @list1 = ('a', 'b', 'c');
my @list2 = ('b', 'c', 'd');

my $lc = List::Compare->new(\@list1, \@list2);

# 積集合 (@list1, @list2 両方の配列に含まれる要素）
my @intersection = $lc->get_intersection;
print "@intersection \n";
 # prints b c

# 和集合（@list1, @list2 のすべての要素から重複を取り除いたもの）
my @union = $lc->get_union;
print "@union \n";
 # prints a b c d

# 差集合 (@list1にのみ含まれる要素)
my @list1only = $lc->get_Lonly;
print "@list1only \n";
 # prints a

# 差集合 (@list2にのみ含まれる要素)
my @list2only = $lc->get_Ronly;
print "@list2only \n";
 # prints d

より詳しくは： http://search.cpan.org/dist/List-Compare/lib/List/Compare.pm

差集合だけで良い場合は Array::Diffでも良いみたい。