[newbie] how to get just the first value of a hash??

[Janek Schleicher]

Guest1 wrote at Wed, 03 Sep 2003 14:52:22 +0100:

You can't.
Hashs are unsorted, so there is no first key or value.


Greetings,
Janek

 

[Janek Schleicher]

Guest1 wrote at Wed, 03 Sep 2003 14:52:22 +0100:

If you want to loop over the values of a hash,
you can either use the list of all values with

my $value = (values %hash)[0];

or iterate through with

while (my ($key, $value) = each %hash) {
# do something with them
}

However, the returned value is in general not the same as the first value
you've written into the hash.


Greetings,
Janek

 

[Guest1]

Thanks in advance
Pedro

 

[Bigus]

There is no "first value of a hash". That is, a hash just consists of keys
and values. If you want the lowest value in a hash, assuming the values are
all numbers of course, then you could do it something like this:

@keys = sort {$hash{$a} <=> $hash{$b}} keys %hash;
print $hash{$keys[0]};

Bigus

 

[Mina Naguib]

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Guest1 wrote:

In the future, please post your question in the body of your message, not just the subject.

Thanks in advance
Pedro

Unlike arrays, hashes are not an ordered list, therefore there's no concept of "first".

Think of a hash as a way to describe someone's face for example. One property is eye colour,
another is hair length, etc. None of the properties are first or last or more important than the other.

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[Gunter Schelfhout]

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Guest1 wrote:

In the future, please post your question in the body of your message, not
just the subject.


Unlike arrays, hashes are not an ordered list, therefore there's no
concept of "first".

Think of a hash as a way to describe someone's face for example. One
property is eye colour,
another is hair length, etc. None of the properties are first or last or
more important than the other.
Ack.

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Is this PGP-sig really nescessary on usenet? It's ugly like hell. And a lot
of work if you want to remove it on reply.

 

[Brian Harnish]

Thanks in advance
Pedro

define first

- Brian

 

[Gunter Schelfhout]

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Mina Naguib wrote: [snip...]

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=+nrC
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Is this PGP-sig really nescessary on usenet? It's ugly like hell. And a lot
of work if you want to remove it on reply.

Yes, it is nescessary, it's the only way of telling who really sent the
message. And, the signatures are roughly the acceptable size for usenet
..sig's.

- Brian Harnish ([email protected])
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=oNJC
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[Gunter Schelfhout]

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Mina Naguib wrote: [snip...]

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jmMWbG/iGJMYyI/BXxfkkLw=
=+nrC
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Is this PGP-sig really nescessary on usenet? It's ugly like hell. And a
lot of work if you want to remove it on reply.

blabla.

Yes, it is nescessary, it's the only way of telling who really sent the
message. And, the signatures are roughly the acceptable size for usenet
.sig's.
blabla

- Brian Harnish ([email protected])
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BDUAWRPfYJqdoTUfOVdhEw0=
=oNJC
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I know where it is used for. IMHO, it doesn't make sense to use it on
usenet.
Look at the mess after only a couple of messages.
- --
Blood, sweat & tears
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[Guest1]

I have a hash of arrays, and I would like to get the length of any of
these arrays. I said first instead to say any of them (because all the
arrays have the same length), More clear my question now?

On the future I will try to be more clear from the begining.

Thanks
P

 

[Uri Guttman]

<don't top post>

G> I have a hash of arrays, and I would like to get the length of any of
G> these arrays. I said first instead to say any of them (because all the
G> arrays have the same length), More clear my question now?

perldoc -f each

G> On the future I will try to be more clear from the begining.

that is always helpful

uri

 

[Gunnar Hjalmarsson]

I have a hash of arrays, and I would like to get the length of any
of these arrays. I said first instead to say any of them (because
all the arrays have the same length), More clear my question now?

Suppose so. Assuming that you by "length" mean the number of elements,
this is one way:

print scalar @{$myhash{(keys %myhash)[0]}};

On the future I will try to be more clear from the begining.

Good. Also, in the future, please don't top post.

 

[John Bokma]

There is no "first value of a hash". That is, a hash just consists of keys
and values. If you want the lowest value in a hash, assuming the values are
all numbers of course, then you could do it something like this:

@keys = sort {$hash{$a} <=> $hash{$b}} keys %hash;
print $hash{$keys[0]};

technically this is O(n log n) while just looping over all keys and
finding the lowest is O(n).

my @keys = keys %hash;
my $min = $hash{shift @keys}; # assign "first" as minimum
foreach my $key (@keys) {
$min = $hash{$key} if $hash{$key} < $min; # try to find better one
}

assuming %hash has values

HTH

 

[Brian Harnish]

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Mina Naguib wrote: [snip...]

Is this PGP-sig really nescessary on usenet? It's ugly like hell. And a
lot of work if you want to remove it on reply.

blabla.

Yes, it is nescessary, it's the only way of telling who really sent the
message. And, the signatures are roughly the acceptable size for usenet
.sig's.
blabla

- Brian Harnish ([email protected])

I know where it is used for. IMHO, it doesn't make sense to use it on
usenet.
Look at the mess after only a couple of messages.
- --
Blood, sweat & tears

Well, we're all entitled to oppinions. I don't think it's difficult to
jump to the end of the message and delete a few lines when replying. And
the only reason it got so ugly in our quoting is because we quoted the
sigs, because thats what we were discussing. Ususally, you strip out any
text that isn't relevant to the conversation (such as pgpsigs). If someone
wants to verify that the quoted message came from the right person, they
can check the original message.

BTW: My news reader doesn't support pgp signing, so I copy/paste sign.
Takes an extra couple of seconds, but I find it worthy, so that people
know w/o a doubt that a message came from me.

- Brian
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[Gunnar Hjalmarsson]

Assuming that you by "length" mean the number of elements,
this is one way:

print scalar @{$myhash{(keys %myhash)[0]}};

or maybe one of these:
print scalar @{ (values %myhash)[0] };
print $#{ (values %myhash)[0] }+1;
print $#{ (each %myhash)[1] }+1;
print @{ (%myhash)[1] }+0;

Yes. TMTOWTDI. But I have to admit that all your suggestions are more
straight-forward than mine. I forgot about the values function. And
each... Oh, well. ;-)

 

[Gunter Schelfhout]

Well, we're all entitled to oppinions.
Certainly.

I don't think it's difficult to
jump to the end of the message and delete a few lines when replying.

And on top.

And
the only reason it got so ugly in our quoting is because we quoted the
sigs, because thats what we were discussing. Ususally, you strip out any
text that isn't relevant to the conversation (such as pgpsigs). If someone
wants to verify that the quoted message came from the right person, they
can check the original message.

OK. I don't have your public key. How should I check it? Via a key-server?
You used my name, but not my headers. These should be enough to check the
postings, no?

BTW: My news reader doesn't support pgp signing, so I copy/paste sign.
Takes an extra couple of seconds, but I find it worthy, so that people
know w/o a doubt that a message came from me.

Maybe you can put it after '-- ', so it will be cut by the readers which has
the option set to cut signatures?

Anyway, enough off-topic postings.

 

[Anno Siegel]

Suppose so. Assuming that you by "length" mean the number of elements,
this is one way:

print scalar @{$myhash{(keys %myhash)[0]}};

or maybe one of these:
print scalar @{ (values %myhash)[0] };
print $#{ (values %myhash)[0] }+1;
print $#{ (each %myhash)[1] }+1;
print @{ (%myhash)[1] }+0;

The "each"-solution is different from the others -- it doesn't expand
all of the hash, which is good. It also leaves the hash with a not-
quite-fresh iterator, which is bad. In a one-off program it probably
doesn't matter, but in a general-purpose routine it would. Where is
uneach?

Anno

 

[Uri Guttman]

AS> The "each"-solution is different from the others -- it doesn't expand
AS> all of the hash, which is good. It also leaves the hash with a not-
AS> quite-fresh iterator, which is bad. In a one-off program it probably
AS> doesn't matter, but in a general-purpose routine it would. Where is
AS> uneach?

it is called keys.

uri

 

[Anno Siegel]

AS> The "each"-solution is different from the others -- it doesn't expand
AS> all of the hash, which is good. It also leaves the hash with a not-
AS> quite-fresh iterator, which is bad. In a one-off program it probably
AS> doesn't matter, but in a general-purpose routine it would. Where is
AS> uneach?

it is called keys.

Yes and no. "keys" resets the iterator. The mythical uneach restores it,
so the next call to each returns what it would have before. A tied hash
could implement it.

Anno

 

[Keith Keller]

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it is called keys.

In scalar context, will keys run through the whole hash? If so,
then it doesn't sound the same as Anno's suggested ''uneach''.

- --keith

- --
(e-mail address removed)-francisco.ca.us
(try just my userid to email me)
AOLSFAQ=http://wombat.san-francisco.ca.us/cgi-bin/fom

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