checking if hashref value exists based on a dynamic array

jonathan415 has asked for the wisdom of the Perl Monks concerning the following question:

I have an hashref that has the following data.

$href = {
           'a'  => {
                     't' => {
                               'x' => {
                                         '2008-08-07' => 1
                                      }
                            }
                   }
            'b'  => {
                      'd' => {
                                'o' => {
                                          '2008-08-06' => 1
                                       }
                             }
                    }
        };
[download]

and I have an array with the following data:

@array = ('a', 't', 'x', '2008-08-07');
[download]

I know that I could see if $href->{a}->{t}->{x}->{2008-08-07} exists by just typing:

if (exists $href->{a}->{t}->{x}->{2008-08-07} ){
    print "href value exists";
}
[download]

But that would be too statically hard encoded and manual.
I am trying to find a more elegant way to see if the hashref exists based on a dynamically generated @array values that aren't known yet.
That way I can generate the exists statement corresponding to whatever the array length and values are instead dynamically. Basically if the array turns out to be:

@array2  = ('b', 't', 'm', 'p');
[download]

I'd like to check if:

$href->{b}->{t}->{m}->{p}
[download]

exists without typing out "b, t, m, p".

Comment on checking if hashref value exists based on a dynamic array Select or Download Code

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Re: checking if hashref value exists based on a dynamic array by Corion (Patriarch) on Aug 08, 2008 at 06:17 UTC
Data::Diver was already recommended to you by ikegami.	[reply]
Re^2: checking if hashref value exists based on a dynamic array by jonathan415 (Novice) on Aug 08, 2008 at 06:36 UTC
ikegami, thanks for recommending Data::Diver. I did take a look at it, and it does answer the question. But the problem with modules is that they do the work, and you don't know how they done it. I was more interested in a ways of mapping data structure myself. My first question was actually very different from this one, and I was able to use the concepts of that answer to solve a more complex problem that I had. Basically, I was interested seeing ways of transversing the data structure and how those values relate to each other. If anyone has any other ways of doing it, I'm interested in seeing it.	[reply]
Re^3: checking if hashref value exists based on a dynamic array by ikegami (Patriarch) on Aug 08, 2008 at 07:10 UTC
But the problem with modules is that they do the work, and you don't know how they done it. Probably something along the lines of the following, with error checking added. `my $p = \$href; $p = \($$p->{$_}) for @keys; $$p = $val;` [download] Update: Oops, the above is code for setting with autovivification (your other question). Checking if the indexes exist without autovivification could be done using `my $p = $href; for (@keys) { return 0 if !exists($p->{$_}); $p = $p->{$_}; } return 1;` [download]	[reply] [d/l] [select]
Re^3: checking if hashref value exists based on a dynamic array by chromatic (Archbishop) on Aug 08, 2008 at 07:01 UTC
But the problem with modules is that they do the work, and you don't know how they done it. The source code is generally available, and many modern modules include decent test suites.	[reply]
Re^3: checking if hashref value exists based on a dynamic array by Anonymous Monk on Aug 08, 2008 at 06:55 UTC
Look inside and you'll know	[reply]
Re: checking if hashref value exists based on a dynamic array by pc88mxer (Vicar) on Aug 08, 2008 at 06:19 UTC
`sub deep_exists { my $hash = shift; return 0 if @_ == 0; while (@_ > 1) { $hash = $hash->{shift} or return 0; } return exists $hash->{$_[0]}; } if (deep_exists(\%hash, 'a', 't', 'etc')) { ... }` [download]	[reply] [d/l]
Re^2: checking if hashref value exists based on a dynamic array by kyle (Abbot) on Aug 08, 2008 at 15:15 UTC
Did you try this? Generally, "`$hash->{shift}`" is interpreted as "`$hash->{'shift'}`", but I think you mean "`$hash->{shift()}`". Also, this and other solutions I've seen here seem to ignore the possibility of running into a non-hash somewhere along the way. use Test::More 'tests' => 5; sub deep_exists { my $hash = shift; my $key = shift; return 0 if ( ref $hash ne ref {} \|\| ! exists $hash->{$key} ); return deep_exists( $hash->{$key}, @_ ) if @_; return 1; } my %h; $h{there}{also}{yes} = 1; $h{hash}{shift}{scalar} = 1; ok( deep_exists( \%h, 'there', 'also', 'yes' ), 'there also yes' ); ok( deep_exists( \%h, 'there', 'also' ), 'there also' ); ok( ! deep_exists( \%h, 'there', 'also', 'no' ), 'there also no' ); ok( deep_exists( \%h, 'hash', 'shift', 'scalar' ), 'hash shift scalar' + ); ok( ! deep_exists( \%h, 'hash', 'shift', 'scalar', 'hash' ), 'hash shift scalar hash' ); [download]	[reply] [d/l] [select]
Re^3: checking if hashref value exists based on a dynamic array by ikegami (Patriarch) on Aug 08, 2008 at 20:32 UTC
Also, this and other solutions I've seen here seem to ignore the possibility of running into a non-hash somewhere along the way Mine (Data::Diver) checks.	[reply]
Re: checking if hashref value exists based on a dynamic array by NetWallah (Canon) on Aug 08, 2008 at 06:32 UTC
Extract/adapt from this code as needed: `my %z=(aa=>{bb=>{cc=>44}});; sub chk{ my ($v,$h)=@_; return 1 unless @$h; return 0 unless exists $v->{my $x=shift @$h}; return chk($v->{$x},$h) } print qq[found\n] if chk(\%z,[qw(aa bb cc)]);` [download] Not the best naming convention - but this is a sample (and it's getting late ...) ... Have you been high today? I see the nuns are gay! My brother yelled to me...I love you inside Ed - Benny Lava, by Buffalax	[reply] [d/l]
Re: checking if hashref value exists based on a dynamic array by localfilmmaker (Novice) on Aug 10, 2008 at 22:58 UTC
One important thing to keep in mind while working with large complex data structure and checking for existence is that some hash entries will be created just by using them. For example, `my %hash = ( a => { ab => { ac => 'yup', }, }, ); # Check for existence if (exists $hash{aa}->{ab}->{ac}) { ## Notice that 'aa' is a typo an doesn't exist ## but will be auto-created and now contain a ## hash ref with one entry 'ab'. print "ac exists.\n"; ## won't get printed } if (exists $hash{aa}) { ## This will succeed because $hash{aa} was auto ## created above. print "aa exists.\n"; ## will get printed }` [download] The `exists` check works on the last part of the data structure and not each step through the data structure. Meaning: `if exists $hash{aa} ## exists doesn't check this ->{ab} ## Nor this ->{ac} ## Ah ha! exists does check here ;` [download] Everything before that last part of the data structure gets auto created if it doesn't exist. Only the last part will not. Just keep that in mind. -spencer	[reply] [d/l] [select]