Re: Pick any key from a very large hash

If you don’t want to use "keys", here is a fancy way to do it.

my %hash = (
    a => 1,
    b => 2,
    c => 3,
    d => 4,
    e => 5,
    f => 6,
    g => 7,
    h => 8,
    i => 9,
    j => 10,    
);

my $hash_length = %hash;
# To get actual length you would need 'scalar keys %hash'
# But we are not using 'keys' here so lets get the length other way 
$hash_length =~ s{/.*}{};
foreach (1...10) {
    my $rand_num = rand $hash_length;
    # Make sure number is even.
    $rand_num = ($rand_num %2) ? ($rand_num - 1) : ($rand_num);
    my $key = (%hash)[$rand_num];
    print "$_\t: $key\n";
}

# output
# 1       : e
# 2       : d
# 3       : c
# 4       : j
# 5       : a
# 6       : e
# 7       : e
# 8       : c
# 9       : j
# 10      : e
[download]

Regards,
Ashish

Comment on Re: Pick any key from a very large hash Download Code

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Re^2: Pick any key from a very large hash by GrandFather (Saint) on Jul 12, 2009 at 05:11 UTC
OP's concern was not the use of keys, but the potential cost of using it due to a perceived 'temporary array'. However various solutions to that problem have been suggested. Let's see how yours stacks up: `use strict; use warnings; use Benchmark qw(cmpthese); my %bigHash = map {$_ => undef} 1 .. 1e3; my ($key) = each %bigHash; my $count = keys %bigHash; my ($key2) = (%bigHash)[0]; print "First key '$key', second '$key2'\n"; cmpthese ( -1, { byEach => sub {scalar keys %bigHash; my ($key) = each %bigHas +h;}, byArray => sub {my $key = (%bigHash)[0]}, } );` [download] Prints: `First key '559', second '559' Rate byArray byEach byArray 5228/s -- -100% byEach 2414187/s 46082% --` [download] It's that 'temporary array' OP was worried about. A fancy solution no doubt but, for saving time, not a good one. True laziness is hard work	[reply] [d/l] [select]
Re^3: Pick any key from a very large hash by ashish.kvarma (Monk) on Jul 12, 2009 at 10:53 UTC
I jumped in without giving it a thought and missed the real problem. I do agree it wouldn’t be efficient therefore won’t solve the purpose. I guess I gotta give some time before jumping in. Regards, Ashish	[reply]
Re^2: Pick any key from a very large hash by FloydATC (Deacon) on Jul 12, 2009 at 06:50 UTC
Still, it's a creative solution to the problem, and within the original domain. I'm sure this technique can be helpful when dealing with a big native hash and not a DB_File. -- Time flies when you don't know what you're doing	[reply]