> "HP" == Harry Putnam writes:
>> ARRAY(0x91af588) convol5.pnm
HP> Finally my google strings hit paydirt and I discovered the use of
HP> @{ $h{$name} }
HP> To get at the content of what is only a reference to a hash. `@' as
HP> used above is said to `dere
Jim Gibson writes:
> my @original_keys = @{$inv_hash{$inverted_key}};
>
> The element of the inverted hash is an array reference. The array is fetched
> (copied into @original_keys) by de-referencing the reference. If there was
> only key with the value $invereted_key, then the array @original_ke
Harry Putnam writes:
> [...]
>
> ARRAY(0x91af588) convol5.pnm
> exits only in rh1
> --- --- ---
> ARRAY(0x91aeb38) .arch-inventory
> exits only in rh1
>
> [...]
>
> How can I get the actual name represented by `ARRAY(0x91af588)' etc?
> Is Da
On 5/9/10 Sun May 9, 2010 1:02 PM, "Harry Putnam"
scribbled:
> Shawn H Corey writes:
>
>
>> my %inv_hash = invert( \%hash );
>> print '%inv_hash: ', Dumper \%inv_hash;
>>
>> This will output:
>>
>> %inv_hash: $VAR1 = {
>> 'f2' => [
>> './b/l/c/f2'
>> ],
>> 'fb' => [
>> '.
Shawn H Corey writes:
> my %inv_hash = invert( \%hash );
> print '%inv_hash: ', Dumper \%inv_hash;
>
> This will output:
>
> %inv_hash: $VAR1 = {
> 'f2' => [
> './b/l/c/f2'
> ],
> 'fb' => [
> './b/fb',
> './b/g/h/r/fb'
> ],
> 'fc' => [
> './b/g/f/r/fc'
> ],
> 'fd
"Uri Guttman" writes:
> as others have shown, that fails because of the dup value of 'fb'. but
> in some cases where you know there are no dups, then reverse is a fine
> solution. it all depends on the data and what you want to see when you
> invert the hash.
Well give the devil his due... you a
Dermot writes:
[...]
> my %inverse_hash = invert( \%hash );
>
> invert() is being passed a reference to the hash. References are a
> useful and efficient way to pass data around [1]. You can create a
> reference by putting a back-slash in front of your data. EG:
[...] snipped more good info
T
Shawn H Corey writes:
First, let me thank you for explaining every one of my questions
simply and fully. Really nice to know there are people who seem to
understand so much of this.
[...]
> my %inv_hash = invert( \%hash );
> print '%inv_hash: ', Dumper \%inv_hash;
>
> This will output:
>
>
> "B" == Brian writes:
>> I have an example from Shawn C. from another thread, presented here
>> out of context. The code does just what he meant it to do.
>> It inverts a hash.
B> Just curious if there is a particular reason Shawn did not use the reverse
function:
B> my %hash
I have an example from Shawn C. from another thread, presented here
out of context. The code does just what he meant it to do.
It inverts a hash.
Just curious if there is a particular reason Shawn did not use the
reverse function:
my %hash = (
'./b/fb'=> 'fb',
'./
> "Brian" == Brian writes:
Brian> Just curious if there is a particular reason Shawn did not use the
reverse function:
Brian> my %hash = (
Brian> './b/fb'=> 'fb',
Brian> './b/c/fd' => 'fd',
Brian> './b/l/c/f2'=> 'f2',
Brian> './b/g/
Brian wrote:
I have an example from Shawn C. from another thread, presented here
out of context. The code does just what he meant it to do.
It inverts a hash.
Just curious if there is a particular reason Shawn did not use the reverse
function:
my %hash = (
'./b/fb'=> 'fb
> I have an example from Shawn C. from another thread, presented here
> out of context. The code does just what he meant it to do.
> It inverts a hash.
Just curious if there is a particular reason Shawn did not use the reverse
function:
my %hash = (
'./b/fb'=> 'fb',
On 9 May 2010 14:26, Harry Putnam wrote:
> I have an example from Shawn C. from another thread, presented here
> out of context. The code does just what he meant it to do.
> It inverts a hash.
>
> I'm trying to understand what is going on inside the sub function
> `invert()'.
>
> --- -
Harry Putnam wrote:
I have an example from Shawn C. from another thread, presented here
out of context. The code does just what he meant it to do.
It inverts a hash.
I'm trying to understand what is going on inside the sub function
`invert()'.
---- ---=--- -
Harry Putnam writes:
[...]
Typo alert:
> It appears the parts to are again flattened into
^a hash
> an array
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I have an example from Shawn C. from another thread, presented here
out of context. The code does just what he meant it to do.
It inverts a hash.
I'm trying to understand what is going on inside the sub function
`invert()'.
---- ---=--- -
m
into the markup,
which now has to be extracted (and you already know my opinion on clever :).
To me, inverting a hash is just another round of Perl Golf, not
something I would use in Real Code. ;)
--
Just my 0.0002 million dollars worth,
Shawn
Programming is as much about organizatio
x27;t
really mean to suggest that any code dealing with hashes should always keep
both the hash and its inverse under all circumstances. So the discussion might
be getting a bit silly.
>As for inverting the return from a database, I would get the database to
>do it.
Oh, absolutely.
>&g
e database to
do it. It can take advantage of relationships inside the database that
are lost when the data is extracted.
So I don't think it is fair to say that inverting a hash is never needed,
although you can certainly minimize the need for it if you build your own
data structures carefull
Uri Guttman stemsystems.com> writes:
> EA> foreach my $k (sort keys %hash) {
>
>why the sort?
No terribly good reason; I just wanted the error messages to be deterministic.
You could speed it up a bit by not sorting and it would still work just as well,
but the error message given might in
It's a question of taste, but I would prefer to just get one
hash as the return value, and invert it if I need to.
So I don't think it is fair to say that inverting a hash is never needed,
although you can certainly minimize the need for it if you build your own
data structures careful
Jenda Krynicky Krynicky.cz> writes:
>
[inverting a hash but checking that no data is lost]
>>To give a really useful error message is a bit more code:
>>
>>my %reverse;
>>foreach my $k (sort keys %hash) {
>>my $v = $hash{$k};
>>if
Jenda Krynicky wrote:
From: "Shawn H. Corey"
push @{ $r{$h{$_}} }, $_ for keys %h; # one line :)
Is it simple enough so that you immediately know what does it do? I
guess not. IMHO it's complex enough to warrant being moved to a named
subroutine. Especially since it forces you to write th
From: "Shawn H. Corey"
> Jenda Krynicky wrote:
> > And if you feel like it, create a function that reverses
> >
> > (a => 1, b => 3, c => 1) => (1 => ['a','c'], 2 => ['b'])
> >
> > That's something that's not a SIMPLE oneliner. Even though of course
> > it's not too complex either.
>
> I thin
> "EA" == Ed Avis writes:
EA> foreach my $k (sort keys %hash) {
why the sort?
uri
--
Uri Guttman -- u...@stemsystems.com http://www.sysarch.com --
- Perl Code Review , Architecture, Development, Training, Support --
- Free Perl Training --- http://p
Jenda Krynicky wrote:
And if you feel like it, create a function that reverses
(a => 1, b => 3, c => 1) => (1 => ['a','c'], 2 => ['b'])
That's something that's not a SIMPLE oneliner. Even though of course
it's not too complex either.
I think it's simple enough:
#!/usr/bin/perl
use strict;
From: Ed Avis
> Jenda Krynicky Krynicky.cz> writes:
>
> >> my %hash = (a => 1, b => 2);
> >> my %reverse = safe_hash_invert %hash; # works fine
> >>
> >> $hash{c} = 1;
> >> %reverse = safe_hash_invert %hash; # throws an error
>
> >I don't think there is and I don't think there'
Jenda Krynicky Krynicky.cz> writes:
>> my %hash = (a => 1, b => 2);
>> my %reverse = safe_hash_invert %hash; # works fine
>>
>> $hash{c} = 1;
>> %reverse = safe_hash_invert %hash; # throws an error
>I don't think there is and I don't think there's a need.
>
>my %hash = (a => 1,
From: Ed Avis
> My question is, does there exist a 'safe hash invert' function in some CPAN
> module? I was imagining something like
>
> my %hash = (a => 1, b => 2);
> my %reverse = safe_hash_invert %hash; # works fine
>
> $hash{c} = 1;
> %reverse = safe_hash_invert %hash; # thr
The standard answer on how to invert a hash, so that keys become values and vice
versa, is to use reverse:
my %reversed = reverse %hash;
The standard answer also mentions some caveats, most importantly that if the
original hash is not one-to-one, then some entries will be lost:
use Data:
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