Need some basic hash help.
OK, I basically need the hash equivalent of the array push function. So, in other words, a way to add a hash pair to the end of a hash.
OK, I basically need the hash equivalent of the array push function. So, in other words, a way to add a hash pair to the end of a hash.
japhy posted this at 05:06 — 25th November 2000.
They have: 161 posts
Joined: Dec 1999
You need to read the 'perldata' documentation. A good place to start is http://www.perldoc.com/.
There is no "beginning" or "end" of a hash -- at least, not one that you are thinking of, or have control over. Hashes return their data in an order that is determined by Perl's source code, not you.
That being said, there is no push() equivalent for hashes. Just create a new key-value pair:
my %hash = (EFnet => 'irc.core.com',
DALnet => 'liberty.nj.us.dal.net',
);
$hash{EFnet} = 'irc.prison.net'; # changing existing value
$hash{Undernet} = 'us.undernet.org'; # adding new pair
Vorm posted this at 06:18 — 25th November 2000.
They have: 62 posts
Joined: May 2000
This is sorta off topic, but don't you have to '' those hash keys Japhy? Or am I wrong again?
Your answer does make sense, I guess I just didn't think out of the box. I mean, it does seem logical that hashes would have a push, doesn't it?
Mark Hensler posted this at 08:16 — 25th November 2000.
He has: 4,048 posts
Joined: Aug 2000
why?
you don't access them by numbers (usually, I guess you could give them # names...), so how would perl know what to name the next 'element'?
japhy posted this at 15:54 — 25th November 2000.
They have: 161 posts
Joined: Dec 1999
If you read the 'perldata' documentation, you'll see:
an identifier within such curlies is forced to be a string,
as is any single identifier within a hash subscript. Our
earlier example, $days{'Feb'} can be written as $days{Feb}
and the quotes will be assumed automatically. But anything
more complicated in the subscript will be interpreted as an
expression.
[...]
It is often more readable to use the => operator between
key/value pairs. The => operator is mostly just a more
visually distinctive synonym for a comma, but it also
arranges for its left-hand operand to be interpreted as a
string--if it's a bareword that would be a legal identifier.
This makes it nice for initializing hashes:
%map = (red => 0x00f,
blue => 0x0f0,
green => 0xf00,
);
Rob Pengelly posted this at 04:19 — 26th November 2000.
They have: 850 posts
Joined: Jul 1999
I wrote a few examples that will hopefully help you better understand hashes.
<strong>example 1</strong>
my %person_vidcard;
$person_vidcard{Frank} = 'Nvidia TNT 2';
$person_vidcard{Alex} = 'Nvidia TNT';
$person_vidcard{Xena} = 'Nvidia Geforce 2';
$person_vidcard{Guy} = 'Voodoo 3';
#Voodoo 3's suck, so we will delete Guy from the list
delete $person_vidcard{Guy};
foreach(sort keys %person_vidcard)
{
print "$_ has a $person_vidcard{$_}\n";
}
output:
Alex has a Nvidia TNT
Frank has a Nvidia TNT 2
Xena has a Nvidia Geforce 2
<strong>example 2</strong>
my %name_age = (
Donna => 45,
Sammy => 32,
Mike => 22
);
#It is Mike's birthday. If he is found in the hash
#1 more year will be added to his age
if(defined $name_age{Mike})
{
print "Mike is ".++$name_age{Mike};
}
output:
Mike is 23
http://www.thehungersite.com - http://www.therainforestsite.com
http://www.ratemymullet.com - Beauty is only mullet deep.
japhy posted this at 04:38 — 26th November 2000.
They have: 161 posts
Joined: Dec 1999
Technically, you should be using exists() to see if a key-value pair is found in a hash:
%hash = ( foo => undef );if ($hash{foo}) { print 1 } # not shown
if (defined $hash{foo}) { print 2 } # still not shown
if (exists $hash{foo}) { print 3 } # shown
if ($hash{bar}) { print 4 } # not shown
if (defined $hash{bar}) { print 5 } # still not shown
if (exists $hash{bar}) { print 6 } # still not shown
Mark Hensler posted this at 05:10 — 1st December 2000.
He has: 4,048 posts
Joined: Aug 2000
thanks japhy, I never knew about those functions... very usefull.
Vorm posted this at 04:56 — 12th December 2000.
They have: 62 posts
Joined: May 2000
I'm not a total hash/Perl novice, I just sometimes miss obvious stuff.
And the Perl manpages, while a good source of data, I feel that they are VERY confusing and hard to understand. That's why I prefer to ask the people hear about stuff.
Want to join the discussion? Create an account or log in if you already have one. Joining is fast, free and painless! We’ll even whisk you back here when you’ve finished.