I have this hash with hashses.
I would like to iterate only the value of '0'.
$VAR1 = {
'1' => {
'192.168.1.1' => '192.168.1.38'
},
'0' => {
'192.168.32.6' => '192.168.32.43'
}
};
The only way I can access it is by creating two foreach my $key (keys(%myhash)) loops:
Can I use:
foreach my $key (keys(%myhash{0})) ## does not work
or directly access the values somehow?
Thanks
First of all, if you are using consecutive integers as keys to a hash then it is likely that you should be using an array instead.
The value of the hash corresponding to key 0 is $dhcpoffers{0} because it is a scalar value. %dhcpoffers{0} is just a syntax error.
You need
for my $key (keys %{ $dhcpoffers{0} }) { ... }
or, if you prefer
my $offer_0 = $dhcpoffers{0};
for my $key (keys %$offer_0) { ... }
Since version 14 of Perl 5, keys will accept a hash reference, so you may be able to write the much cleaner
for my $key (keys $dhcpoffers{0}) { ... }
Related
I have a hash that looks like this:
my $hash = {
level1_f1 => {
level2_f1 => 'something',
level2_f2 => 'another thing'
},
level1_f2 => {
level2_f3 => 'yet another thing',
level2_f4 => 'bla bla'
level2_f5 => ''
}
...
}
I also got a list of values that correspond to the "level2" keys, which I want to know if thy exist in the hash.
#list = ("level2_f2", "level2_f4", "level2_f99")
I don't know which "level1" key each element of #list belongs to. The only way of finding if they existed I could think was using a foreach loop to go through #list, another foreach loop to go through the keys of %hash and checking
foreach my $i (#array) {
foreach my $k (keys %hash) {
if (exists $hash{$k}{$list[$i]})
}
}
but I wanted to know if there is a more eficient or maybe a more elegant way to do it. All the answers I found ask you to know the "level1" key, which I don't.
Thanks!!
Use values:
for my $inner_hash (values %$hash) {
say grep exists $inner_hash->{$_}, #list;
}
You have to loop all the level1 keys. But if you don't need to know which keys match and merely care for the existence of any, then you don't have to ask for each member of your list explicitly. You could say
foreach my $k (keys %hash) {
if ( #{ $hash{$k} }{ #list } )
{
}
}
The hash slice will return all values in the subhash which have matching keys in the list. Keys in the list that are not in the subhash get ignored.
Note however, that this does potentially more work than you may really need.
You don't need to iterate over "the entire hash".
You will necessarily over the elements of the outer hash since you want to check the value of each one, but you don't need to iterate over the elements of the inner hashes. Your solution already demonstrates that.
So your solution is as efficient as it can be, at least in terms of how well it scales. You can only perform small optimizations such as stopping as soon as a match is found.
for my $i (#list) {
while ( my (undef, $inner) = each(%hash) ) {
if (exists($inner->{$i}) {
...
last;
}
}
keys(%hash); # Reset iterator since it might not be exhausted.
}
As a micro optimization, it might be beneficial to invert the nesting of the loops.
my %list = map { $_ => 1 } #list;
while ( my (undef, $inner) = each(%hash) ) {
while (defined( my $k = each(%$inner) )) {
if ($list{$k}) {
delete($list{$k});
...
last if !keys(%list);
}
}
keys(%$inner); # Reset iterator since it might not be exhausted.
last if !keys(%list);
}
keys(%hash); # Reset iterator since it might not be exhausted.
If the hashes are small, these changes might actually slow things down.
Honestly, if there's truly a speed issue, the problem is that you used the wrong data structure for the type of query you want to run on it!
my %number_words = hash_a_file($_);
foreach my $key ( keys %number_words ) {
++$word_list{$key};
}
This is working but I would like to avoid using the intermediate variable
like this
foreach my $key ( keys hash_a_file($_) ) {
++$word_list{$key};
}
I tried to use refs but still failed. Any way to do this ? Thanks !
The thing is, a subroutine doesn't return a hash. It returns a list. In your original code, it only becomes a hash when you store it in a hash variable.
But there are other ways to create a hash from a list. You can create an anonymous hash and then de-reference it. It's ugly, but it works.
# Inner braces create an anonymous hash.
# Outer braces de-reference that into a "real" hash
foreach my $key ( keys %{ { hash_a_file($_) } } ) {
++$word_list{$key};
}
Update: To back up Borodin's comment, I should add that if this code was presented to me in a code review, I'd suggest rewriting it to use an explicit hash variable as your original code does.
Return a hashref, so that you can form a valid argument for keys (instead of a list)
sub hash_a_file { return { a => 1, b => 2 } }
foreach my $key ( keys %{ hash_a_file() } ) {
say $key
}
I'm rather inexperienced with hashes of hashes - so I hope someone can help a newbie...
I have the following multi-level hash:
$OCRsimilar{$ifocus}{$theWord}{"form"} = $theWord;
$OCRsimilar{$ifocus}{$theWord}{"score"} = $OCRscore;
$OCRsimilar{$ifocus}{$theWord}{"distance"} = $distance;
$OCRsimilar{$ifocus}{$theWord}{"similarity"} = $similarity;
$OCRsimilar{$ifocus}{$theWord}{"length"} = $ilength;
$OCRsimilar{$ifocus}{$theWord}{"frequency"} = $OCRHashDict{$ikey}{$theWord};
Later, I need to sort each second-level element ($theWord) according to the score value. I've tried various things, but have failed so far. The problem seems to be that the sorting introduces new empty elements in the hash that mess things up.
What I have done (for example - I'm sure this is far from ideal):
my #flat = ();
foreach my $key1 (keys { $OCRsimilar{$ifocus} }) {
push #flat, [$key1, $OCRsimilar{$ifocus}{$key1}{'score'}];
}
for my $entry (sort { $b->[1] <=> $a->[1] } #flat) {
print STDERR "#$entry[0]\t#$entry[1]\n";
}
If I check things with Data::Dumper, the hash contains for example this:
'uroadcast' => {
'HASH(0x7f9739202b08)' => {},
'broadcast' => {
'frequency' => '44',
'length' => 9,
'score' => '26.4893274374278',
'form' => 'broadcast',
'distance' => 1,
'similarity' => 1
}
}
If I don't do the sorting, the hash is fine. What's going on?
Thanks in advance for any kind of pointers...!
Just tell sort what to sort on. No other tricks are needed.
#!/usr/bin/perl
use warnings;
use strict;
my %OCRsimilar = (
focus => {
word => {
form => 'word',
score => .2,
distance => 1,
similarity => 1,
length => 4,
frequency => 22,
},
another => {
form => 'another',
score => .01,
distance => 1,
similarity => 1,
length => 7,
frequency => 3,
},
});
for my $word (sort { $OCRsimilar{focus}{$a}{score} <=> $OCRsimilar{focus}{$b}{score} }
keys %{ $OCRsimilar{focus} }
) {
print "$word: $OCRsimilar{focus}{$word}{score}\n";
}
Pointers: perlreftut, perlref, sort.
What seems suspicious to me is this construct:
foreach my $key1 (keys { $OCRsimilar{$ifocus} }) {
Try dereferencing the hash, so it becomes:
foreach my $key1 (keys %{ $OCRsimilar{$ifocus} }) {
Otherwise, you seem to be creating an anonymous hash and taking the keys of it, equivalent to this code:
foreach my $key1 (keys { $OCRsimilar{$ifocus} => undef }) {
Thus, I think $key1 would equal $OCRsimilar{$ifocus} inside the loop. Then, I think Perl will do auto-vivification when it encounters $OCRsimilar{$ifocus}{$key1}, adding the hash reference $OCRsimilar{$ifocus} as a new key to itself.
If you use warnings;, the program ought to complain Odd number of elements in anonymous hash.
Still, I don't understand why Perl doesn't do further auto-vivication and add 'score' as the key, showing something like 'HASH(0x7f9739202b08)' => { 'score' => undef }, in the Data dump.
my $memType = [];
my $portOp = [];
my $fo = "aster.out.DRAMA.READ.gz";
if($fo =~/aster.out\.(.*)\.(.*)\.gz/){
push (#{$memType},$1);
push (#{$portOp},$2);
}
print Dumper #{$memType};
foreach my $mem (keys %{$portCapability->{#{$memType}}}){
//How to use the array ref memType inside a hash//
print "entered here\n";
//cannot post the rest of the code for obvious reasons//
}
I am not able to enter the foreach loop . Can anyone help me fix it?
Sorry this is not the complete code . Please help me.
%{$portCapability->{#{$memType}}}
This doesn't do what you may think it means.
You treat $portCapability->{#{$memType}} as a hash reference.
The #{$memType} is evaluated in scalar context, thus giving the size of the array.
I aren't quite sure what you want, but would
%{ $portCapability->{ $memType->[0] } }
work?
If, however, you want to slice the elements in $portCapability, you would need somethink like
#{ $portCapability }{ #$memType }
This evaluates to a list of hashrefs. You can then loop over the hashrefs, and loop over the keys in an inner loop:
for my $hash (#{ $portCapability }{ #$memType }) {
for my $key (keys %$hash) {
...;
}
}
If you want a flat list of all keys of the inner hashes, but don't need the hashes themselves, you could shorten above code to
for my $key (map {keys %$_} #{ $portCapability }{ #$memType }) {
...;
}
I think what you want is this:
my $foo = {
asdf => {
a => 1, b => 2,
},
foo => {
c => 3, d => 4
},
bar => {
e => 5, f => 6
}
};
my #keys = qw( asdf foo );
foreach my $k ( map { keys %{ $foo->{$_} } } #keys ) {
say $k;
}
But you do not know which of these $k belongs to which key of $foo now.
There's no direct way to get the keys of multiple things at the same time. It doesn't matter if these things are hashrefs that are stored within the same hashref under different keys, or if they are seperate variables. What you have to do is build that list yourself, by looking at each of the things in turn. That's simply done with above map statement.
First, look at all the keys in $foo. Then for each of these, return the keys inside that element.
my $memType = [];
my $portOp = [];
my $fo = “aster.out.DRAMA.READ.gz”;
if ($fo =~ /aster.out\.(\w+)\.(\w+)\.gz/ ) { #This regular expression is safer
push (#$memType, $1);
push (#$portOp, $2);
}
print Dumper “#$memType”; #should print “DRAMA”
#Now if you have earlier in your program the hash %portCapability, your code can be:
foreach $mem (#$memType) {
print $portCapability{$mem};
}
#or if you have the hash $portCapability = {…}, your code can be:
foreach $mem (#$memType) {
print $portCapability->{$mem};
}
#Hope it helps
I have a question I'm hoping you could help with as I am new to hashes and hash reference stuff?
I have the following data structure:
$VAR1 = {
'http://www.superuser.com/' => {
'difference' => {
'http://www.superuser.com/questions' => '10735',
'http://www.superuser.com/faq' => '13095'
},
'equal' => {
'http://www.superuser.com/ ' => '20892'
}
},
'http://www.stackoverflow.com/' => {
'difference' => {
'http://www.stackoverflow.com/faq' => '13015',
'http://www.stackoverflow.com/questions' => '10506'
},
'equal' => {
'http://www.stackoverflow.com/ ' => '33362'
}
}
If I want to access all the URLs in the key 'difference' so I can then perform some other actions on the URLs, what is the correct or preferred method of accessing those elements?
e.g I will end up with the following URLs that I can then do stuff to in a foreach loop with:
http://www.superuser.com/questions
http://www.superuser.com/faq
http://www.stackoverflow.com/faq
http://www.stackoverflow.com/questions
------EDIT------
Code to access the elements further down the data structure shown above:
my #urls;
foreach my $key1 ( keys( %{$VAR1} ) ) {
print( "$key1\n" );
foreach my $key2 ( keys( %{$VAR1->{$key1}} ) ) {
print( "\t$key2\n" );
foreach my $key3 ( keys( %{$VAR1->{$key1}{$key2}} ) ) {
print( "\t\t$key3\n" );
push #urls, keys %{$VAR1->{$key1}{$key2}{$key3}};
}
}
}
print "#urls\n";
Using the code above why do I get the following error?
Can't use string ("13238") as a HASH ref while "strict refs" in use at ....
It is not difficult, just take the second level of keys off every key in the variable:
my #urls;
for my $key (keys %$VAR1) {
push #urls, keys %{$VAR1->{$key}{'difference'}};
}
If you're struggling with dereferencing, just keep in mind that all values in a hash or array can only be a scalar value. In a multilevel hash or array the levels are just single hashes/arrays stacked on top of each other.
For example, you could do:
for my $value (values %$VAR1) {
push #urls, keys %{$value->{'difference'}};
}
Or
for my $name (keys %$VAR1) {
my $site = $VAR1->{$name};
push #urls, keys %{$site->{'difference'}};
}
..taking the route either directly over the value (a reference to a hash) or over a temporary variable, representing the value via the key. There is more to read in perldoc perldata.