如何从数组中减去数组? [英] How to subtract an array from an array?

问题描述

当我尝试以下时

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my @bl = qw(red green blue);
my @a = qw(green yellow purple blue pink);

print Dumper [grep {not @bl} @a];

我得到一个空数组.我本来希望从 @a 中减去 @bl，所以输出是 yellow Purple pink.

I get an empty array. I would have expected that @bl was subtracted from @a, so the output was yellow purple pink.

这里出了什么问题?

推荐答案

需要将@bl转成hash来进行集差:

You need to turn @bl into a hash to perform the set difference:

my %in_bl = map {$_ => 1} @bl;
my @diff  = grep {not $in_bl{$_}} @a;

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