CODEWITHSUNDEEP
perl
len8200
len8200

Reputation: 85

How to find out if there is at least one key in a hash

There is such a hash:

$hash = { Apple => 'red', Lemon => 'yellow', Carrot => 'orange' }

How do you know if there is at least one key in the hash?

Upvotes: 2

Views: 186

Answers (4)

amit bhosale
amit bhosale

Reputation: 482

Above mentioned methods are good. But if you want more information about hash you can use https://metacpan.org/pod/Hash::Util module.

bucket_info method : Return a set of basic information about a hash.

  • 0: Number of keys in the hash
  • 1: Number of buckets in the hash
  • 2: Number of used buckets in the hash
  • rest : list of counts, Kth element is the number of buckets with K keys in it.

Code

use strict;
use warnings;
use Hash::Util qw(bucket_info);

my $hash = { Apple => 'red', Lemon => 'yellow', Carrot => 'orange' };
my $empty_hash = {};

my ($keys, $buckets, $used, @length_counts)= bucket_info($hash);

print "\n Number of keys $keys in the hash \n";
print "\n Number of buckets $buckets in the hash \n";
print "\n Number of used buckets $used in the hash \n";

((bucket_info($hash))[0]) ? print "\n Not Empty hash" : print "\n Empty hash";

((bucket_info($empty_hash))[0]) ? print "\n Not Empty hash" : print "\n Empty hash";

output

Number of keys 3 in the hash

 Number of buckets 8 in the hash

 Number of used buckets 2 in the hash

 Not Empty hash
 Empty hash

Upvotes: 1

ikegami
ikegami

Reputation: 385685

Simply using the hash in scalar context will suffice.

if (%hash) {         # Or %$hash in your case.
   say "Not empty";
} else {
   say "Empty";
}

%hash vs keys(%hash)

  • keys(%hash) in scalar context: Returns the number of elements.
  • %hash in scalar context (≥5.26): Returns the number of elements.
  • %hash in scalar context (<5.26): Returns whether the hash is empty or not.

So, no matter the version, you can always simply use %hash in scalar context to check if a hash is empty. keys(%hash) can be used to achieve the same result, but %hash in boolean context (e.g. if (%hash)) has been faster than an equivalent use of keys(%hash) since 5.12.

So, no matter the version, you can always simply use keys(%hash) in scalar context to get the number of elements in the hash. You can also use %hash in scalar context in newer versions.

Upvotes: 3

mpapec
mpapec

Reputation: 50637

Hash returns non-false value in scalar context when populated, or key - value pairs in list context.

You can simply check if it is not empty with,

if (%$hash)...

Upvotes: 1

vkk05
vkk05

Reputation: 3222

You can decide the hash key size using: scalar keys(%hash). Based on the size your check can be done below:

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my %hash = ( 
    Apple  => 'red', 
    Lemon  => 'yellow', 
    Carrot => 'orange'
);

print Dumper(\%hash);

print "Size:".scalar keys(%hash)."\n";

if(scalar keys(%hash) > 0){
    print "Hash size is greater than 1\n";
} else {
    print "Hash size is zero\n";
}

Upvotes: 1

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