I have an array of structs (from Class::Struct) and I am having trouble accessing their 'fields'. I've looked at other solutions such as Perl - Class::Struct Deferencing array and Perl documentation without success. My code is:
use Class::Struct;
use Data::Dump qw(dump);
struct( Tag => {
attributes => '%',
value => '$'
});
my #data = [];
push #data, Tag->new(attributes => { 'id' => 1 }, value => "hello world!");
dump #data;
my $tag = $data[0];
my $value = $tag->value;
print $value, "\n";
I've tried variations on blessing $tag with 'Tag' (since can't call value on unblessed ... is the current error), dereferencing $tag as a hash, and more.
Your error is in initialization of #data:
my #data = []; # the same as my #data = ( [] );
You declare array called #data and initialize it with one empy array ref.
Next you push second element to array using push. Your class now in $data[1].
So fixed example:
struct( Tag => {
attributes => '%',
value => '$'
});
my #data;
push #data, Tag->new(attributes => { 'id' => 1 }, value => "hello world!");
my $tag = $data[0];
my $value = $tag->value;
print $value, "\n";
Related
I have an array of hashrefs built from a database using fethrow_hashref(). The data structure is built like so:
while (my $ref = $sth->fetchrow_hashref()) {
push #lines, $ref;
}
I sort the data in the query by program name ascending, so all of the references in the array are still in alphabetical order. Then, I go through each hash and find the value that is numerically equal to a '1'. I then take the caolumn name, and store it to compare to the rest of the hashrefs with that program name to ensure they all have a '1' in the same column.
my $pgm = "";
my $met_lvl = "";
my #devs = ();
my %errors = ();
my $error = "";
foreach my $line_ref (#lines) {
if ($pgm ne $line_ref->{"PROGRAM"}) {
if (#devs && $error) {
# print " Different number metal layers for $pgm: #devs \n";
$error = "";
}
#devs = ();
$pgm = $line_ref->{"PROGRAM"};
($met_lvl) = grep { $line_ref->{$_} == 1 } keys(%$line_ref);
push #devs, $line_ref->{"DEVICE"};
} elsif ($pgm eq $line_ref->{"PROGRAM"}) {
push #devs, $line_ref->{"DEVICE"};
my ($met_chk ) = grep { $line_ref->{$_} == 1 } keys(%$line_ref);
if ($met_chk ne $met_lvl) {
$errors{$line_ref->{"PROGRAM"}} = $line_ref->{"PROGRAM"};
$error = "YUP";
}
}
}
I'd like to be able to access the hashrefs individually, based on matching column names from the database. How can I access the hashrefs with "TEST" values for "PROGRAM" keys? I used Data::Dumper to provide an example of a few of the hashrefs I'd like to access based on "PROGRAM" value:
'PLM' => undef,
'SLM' => undef,
'QLM' => undef,
'DEVICE' => 'DEV1',
'TLM' => '1',
'DLM' => undef,
'ROUTING' => 'NORMAL',
'PROGRAM' => 'TEST'
};
$VAR455 = {
'PLM' => undef,
'SLM' => undef,
'QLM' => undef,
'DEVICE' => 'DEV2',
'TLM' => '1',
'DLM' => undef,
'ROUTING' => 'NORMAL',
'PROGRAM' => 'TEST'
};
$VAR456 = {
'PLM' => undef,
'SLM' => undef,
'QLM' => undef,
'DEVICE' => 'DEV3',
'TLM' => '1',
'DLM' => undef,
'ROUTING' => 'NON_STANDARD',
'PROGRAM' => 'EXP'
};
$VAR457 = {
'PLM' => undef,
'SLM' => undef,
'QLM' => undef,
'DEVICE' => 'DEV4',
'TLM' => '1',
'DLM' => undef,
'ROUTING' => 'NORMAL',
'PROGRAM' => 'FINAL'
};
I'd like to be able to access key values for the hashrefs which contain the same program name. I cannot even begin to figure out what type of operation to use for this. I assume map is the correct way to do it, but dereferencing the "PROGAM" value for each element (hashref) in the array is beyond the scope of my understanding. I hope I was able to define the problem well enough for you guys to be able to help.
Edit: The impetus for wanting to access hashrefs with the same 'PROGRAM" value is to be able to provide an output of selected values to print to a logfile. So, after I compare and find differences between those hashrefs with the same "PROGRAM" value, I want to access them all again, and print out the desired column values to the lofgile.
Looks like you need to exrtact subsets of your data (hashrefs) with the same PROGRAM name.
Can preprocess your data to build a hash with those names as keys, and arrayrefs (with suitable hashrefs) as values. Then process those groups one at a time.
use warnings;
use strict;
use feature 'say';
use Data::Dumper; # to print complex data below
... populate #lines with hashrefs as in the question or copy-paste a sample
# Build hash: ( TEST => [ hashrefs w/ TEST ], EXP => [ hashrefs w/ EXP ], ... )
my %prog_subset;
for my $hr (#lines) {
push #{ $prog_subset{$hr->{PROGRAM}} }, $hr;
# Or, using "postfix dereferencing" (stable from v5.24)
# push $prog_subset{$hr->{PROGRAM}}->#*, $hr;
}
foreach my $prog (keys %prog_subset) {
say "\nProcess hashrefs with PROGRAM being $prog";
foreach my $hr (#{ $prog_subset{$prog} }) {
say Dumper $hr;
}
}
(See postfix dereference)
Now %prog_subset contains keys TEST, EXP, FINAL (and whatever other PROGRAM names are in data), each having for value an arrayref of all hashrefs which have that PROGRAM name.
There are other ways, and there are libraries that can be leveraged, but this should do it.
OK! I found an example of this with the google machine. I replaced #lines = (); with $lines = [];. This allowed me to change the grep statement to (#found) = grep { $pgm eq $_->{PROGRAM} } #$lines;. Now the returned array is a list of the hashrefs that share the program name I'm looking for. Thanks for the help #zdim!
I have a data structure that I got from this code.
my $name = $data->{Instances}->[0]->{Tags};
That data structure looks like this
$VAR1 = [
{
'Key' => 'Name',
'Value' => 'fl-demo'
},
{
'Value' => 'FL',
'Key' => 'state'
}
];
I'm trying to print the keys and values with this
foreach my $key (sort keys %$name) {
my $value = $name->{$key};
print "$key => $value\n";
}
I'm getting
Not a HASH reference at ./x.pl line 19.
The tags are returned as an array, not a hash. So you're looking at doing something like this, instead, to iterate over them:
foreach my $tag (#$name) {
my $key = $tag->{Key};
my $val = $tag->{Value};
print "$key => $val\n";
}
The data structure dump of variable $name indicates that you have array reference.
You can use loop to output the data of interest, do not forget to dereference $name variable.
use strict;
use warnings;
use feature 'say';
my $name = [
{
'Key' => 'Name',
'Value' => 'fl-demo'
},
{
'Value' => 'FL',
'Key' => 'state'
}
];
say "$_->{Key} = $_->{Value}" for #$name;
Output
Name = fl-demo
state = FL
Elaborating on a previous answer:
$name is a reference to an array containing references to hashes.
#$name and #{$name} (equivalent representations) refer to the array that $name references.
${$name}[0] and $name->[0] (equivalent representations) refer to the first hash in the array referenced by $name.
${$name}[0]{'Key'}, $name->[0]->{'Key'}, etc. (equivalent representations) refer to 'Key''s hash value in the first hash in the array referenced by $name.
As such, the following would iterate over all array and hash elements:
foreach my $hashref ( #{$name} )
{
foreach my $key ( sort(keys(%{$hashref})) )
{
printf("%s => %s\n",$key,$hashref->{$key});
}
print "\n";
}
Or, more compactly (and arguably unreadably):
printf("%s\n",join("\n", map {
my $h = $_;
join(', ', map { sprintf('%s=%s',$_,$h->{$_}) } sort(keys(%{$h})) );
} #{$name} ));
I have a string as input, say apple.mango.orange = 100
I also have a hash reference:
$inst = {
'banana' => 2,
'guava' => 3,
'apple' => {
'mango' => {
'orange' => 80
}
}
};
I want to modify the value of orange using the input string. Can someone please help me how I could do this?
I tried splitting the string into (key, value) pair. I then did the following on the key string:
my $key2 = "\$inst->{".$key."}";
$key2 =~ s/\./}->{/g;
$$key2 = $value;
This does not work as intended. Can someone help me out here? I have read the Perl FAQ about not using a variable value as variable but I am unable to think of an alternative.
You are building string that consists of (buggy) Perl code, but you never ask Perl to execute it. ...but that's not the right approach.
sub dive_val :lvalue {
my $p = \shift;
$p = \($$p->{$_}) for #_;
$$p
}
my #key = split /\./, "apple.mango.orange";
dive_val($inst, #key) = $value;
or
use Data::Diver qw( DiveVal );
my #key = split /\./, "apple.mango.orange";
DiveVal($inst, map \$_, #key) = $value;
Not only is a symbolic reference a very bad idea here, it doesn't even solve your problem. You're building an expression in $key2, and just jamming another dollar sign in front of its name won't make perl execute that code. For that you would need eval, which is another bad idea
You can install and use the Data::Diver module, which does exactly this sort of thing, or you can simply loop over the list of hash keys, picking up a new hash reference each time and assigning the value to the element with the last key
The biggest issue is actually parsing the incoming string into a list of keys and a value. This code implements a subroutine apply which applies the implied operation in the string to a nested hash. Unless you are confident of your data, it needs some error checking addingto make sure each of the keys in the list exists. The Data:;Dumper output is just to demonstrate the validity of the result
use strict;
use warnings 'all';
use Data::Dumper;
my $inst = { 'banana' => 2, 'guava' => 3, 'apple' => { 'mango' => { 'orange' => 80 } } };
my $s = 'apple.mango.orange = 100';
apply($s, $inst);
print Dumper $inst;
sub apply {
my ($operation, $data) = #_;
my ($keys, $val) = $operation =~ /([\w.]+)\s*=\s*(\d+)/;
my #keys = split /\./, $keys;
my $last = pop #keys;
my $hash = $data;
$hash = $hash->{$_} for #keys;
$hash->{$last} = $val;
}
output
$VAR1 = {
'banana' => 2,
'apple' => {
'mango' => {
'orange' => '100'
}
},
'guava' => 3
};
This may be something very simple for you but i have been trying for it for more than one hour.
Ok.. Here is my code,
#collection = [
{
'name' => 'Flo',
'model' => '23423',
'type' => 'Associate',
'id' => '1-23928-2392',
'age' => '23',
},
{
'name' => 'Flo1',
'model' => '23424',
'type' => 'Associate2',
'id' => '1-23928-23922',
'age' => '25',
}];
foreach my $row (#collection) {
$build_status = $self->build_config($row);
}
sub build_config {
my $self = shift;
my %collect_rows = #_;
#my %collect_rows = shift;
print Dumper %collect_rows; exit;
exit;
}
Where $row is really an Hash. But when i Print it.. It gives output like below (I am using Dumper),
$VAR1 = 'HASH(0x20a1d68)';
You are confusing references with hashes and arrays.
An array is declared with:
my #array = (1, 2, 3);
A hash is declared with:
my %hash = (1 => 2, 3 => 4);
That's because both hashes and arrays are simply lists (fancy lists, but I digress). The only time you need to use the [] and {} is when you want to use the values contained in the list, or you want to create a reference of either list (more below).
Note that the => is just a special (ie. fat) comma, that quotes the left-hand side, so although they do the same thing, %h = (a, 1) would break, %h = ("a", 1) works fine, and %h = (a => 1) also works fine because the a gets quoted.
An array reference is declared as such:
my $aref = [1, 2, 3];
...note that you need to put the array reference into a scalar. If you don't and do it like this:
my #array = [1, 2, 3];
... the reference is pushed onto the first element of #array, which is probably not what you want.
A hash reference is declared like this:
my $href = {a => 1, b => 2};
The only time [] is used on an array (not an aref) is when you're using it to use an element: $array[1];. Likewise with hashes, unless it's a reference, you only use {} to get at a key's value: $hash{a}.
Now, to fix your problem, you can keep using the references with these changes:
use warnings;
use strict;
use Data::Dumper;
# declare an array ref with a list of hrefs
my $collection = [
{
'name' => 'Flo',
...
},
{
'name' => 'Flo1',
...
}
];
# dereference $collection with the "circumfix" operator, #{}
# ...note that $row will always be an href (see bottom of post)
foreach my $row (#{ $collection }) {
my $build_status = build_config($row);
print Dumper $build_status;
}
sub build_config {
# shift, as we're only accepting a single param...
# the $row href
my $collect_rows = shift;
return $collect_rows;
}
...or change it up to use non-refs:
my #collection = (
{
'name' => 'Flo',
...
},
{
'name' => 'Flo1',
...
}
);
foreach my $row (#collection) {
my $build_status = build_config($row);
# build_config() accepts a single href ($row)
# and in this case, returns an href as well
print Dumper $build_status;
}
sub build_config {
# we've been passed in a single href ($row)
my $row = shift;
# return an href as a scalar
return $row;
}
I wrote a tutorial on Perl references you may be interested in guide to Perl references. There's also perlreftut.
One last point... the hashes are declared with {} inside of the array because they are indeed hash references. With multi-dimentional data, only the top level of the structure in Perl can contain multiple values. Everything else underneath must be a single scalar value. Therefore, you can have an array of hashes, but technically and literally, it's an array containing scalars where their value is a pointer (reference) to another structure. The pointer/reference is a single value.
I have a query string like this:
id=60087888;jid=16471827;from=advance;action=apply
or it can be like this :
id=60087888&jid=16471827&from=advance&action=apply
Now from this i want to create a hash that will have key as id and its value
I have done this
my %in;
$buffer = 'resid=60087888;jobid=16471827;from=advance;action=apply';
#pairs = split(/=/, $buffer);
foreach $pair (#pairs){
($name, $value) = split(/=/, $pair);
$in{$name} = $value;
}
print %in;
But the issue is in the query string it can be semin colon or & so how can we do this please help me
Don't try to solve it with new code; this is what CPAN modules are for. Specifically in this case, URI::Query
use URI::Query;
use Data::Dumper;
my $q = URI::Query->new( "resid=60087888;jobid=16471827;from=advance;action=apply" );
my %hash = $q->hash;
print Dumper( \%hash );
Gives
{ action => 'apply',
from => 'advance',
jobid => '16471827',
resid => '60087888' }
You've already an answer that works - but personally I might tackle it like this:
my %in = $buffer =~ m/(\w+)=(\w+)/g;
What this does is use regular expressions to pattern match either side of the equals sign.
It does so in pairs - effectively - and as a result is treated by a sequence of key-values in the hash assignment.
Note - it does assume you've not got special characters in your keys/values, and that you have no null values. (Or if you do, they'll be ignored - you can use (\w*) instead if that's the case).
But you get:
$VAR1 = {
'from' => 'advance',
'jid' => '16471827',
'action' => 'apply',
'id' => '60087888'
};
Alternatively:
my %in = map { split /=/ } split ( /[^=\w]/, $buffer );
We split using 'anything that isn't word or equals' to get a sequence, and then split on equals to make the same key-value pairs. Again - certain assumptions are made about valid delimiter/non-delimiter characters.
Check this answer:
my %in;
$buffer = 'resid=60087888;jobid=16471827;from=advance;action=apply';
#pairs = split(/[&,;]/, $buffer);
foreach $pair (#pairs){
($name, $value) = split(/=/, $pair);
$in{$name} = $value;
}
delete $in{resid};
print keys %in;
I know I'm late to the game, but....
#!/usr/bin/perl
use strict;
use CGI;
use Data::Dumper;
my $query = 'id=60087888&jid=16471827&from=advance&action=apply&blank=¬_blank=1';
my $cgi = CGI->new($query);
my %hash = $cgi->Vars();
print Dumper \%hash;
will produce:
$VAR1 = {
'not_blank' => '1',
'jid' => '16471827',
'from' => 'advance',
'blank' => '',
'action' => 'apply',
'id' => '60087888'
};
Which has the added benefit of dealing with keys that might not have values in the source string.
Some of the other examples will produce:
$VAR1 = {
'id' => '60087888',
'1' => undef,
'jid' => '16471827',
'from' => 'advance',
'blank' => 'not_blank',
'action' => 'apply'
};
which may not be desirable.
I would have used URI::Query #LeoNerd 's answer, but I didn't have the ability to install a module in my case and CGI.pm was handy.
also, you could
my $buffer = 'id=60087888&jid=16471827&from=advance&action=apply';
my %hash = split(/&|=/, $buffer);
which gives:
$hash = {
'jid' => '16471827',
'from' => 'advance',
'action' => 'apply',
'id' => '60087888'
};
This is VERY fragile, so I wouldn't advocate using it.