array to hash in perl - perl

Question

I have a source list from which I am picking up random items and populating the destination list. The item that are in the list have a particular format. For example:
item1{'name'}
item1{'date'}
etc and many more fields.
while inserting into the destination list I check for unique names on items and insert it into that list. For this I have to traverse the entire destination list to check if an item with a given name exists and if not insert it.
I thought it would be nice if I make the destination list as hash instead of a list again so that I can look up for the item faster and efficiently. I am new to Perl and am not getting how to do this. Anybody, Please help me on how to insert an item, find for a particular item name, and delete an item in hash?
How can I make both the name and date as key and the entire item as value?

Answer 1

my %hash;
Insert an item $V with a key $K?
$hash{$K} = $V
Find for a particular name / key $K?
if (exists $hash{$K}) {
print "it is in there with value '$hash{$K}'\n";
} else {
print "it is NOT in there\n"
}
Delete a particular name / key?
delete $hash{$K}
Make name and date as key and entire item as value?
Easy Way: Just string everything together
set: $hash{ "$name:$date" } = "$name:$date:$field1:$field2"
get: my ($name2,$date2,$field1,$field2) = split ':', $hash{ "$name:$date" }
del: delete $hash{ "$name:$date" }
Harder Way: Store as a hash in the hash (google "perl object")
set:
my %temp;
$temp{"name"} = $name;
$temp{"date"} = $date;
$temp{"field1"} = $field1;
$temp{"field2"} = $field2
$hash{"$name:$date"} = \$temp;
get:
my $find = exists $hash{"$name:$date"} ? $hash{"$name:$date"} : undef;
if (defined find) { # i.e. it was found
printf "field 1 is %s\n", $find->{"field1"}
} else {
print "Not found\n";
}
delete:
delete $hash{"$name:$date"}

Answer 2

It is not easy to understand what you are asking because you do not describe the input and the desired outputs specifically.
My best guess is something along the lines of:
#!/usr/bin/perl
use strict; use warnings;
my #list = (
q(item1{'name'}),
q(item1{'date'}),
);
my %lookup;
for my $entry ( #list ) {
my ($name, $attrib) = $entry =~ /([^{]+){'([^']+)'}/;
$lookup{ $name }{ $attrib } = $entry;
}
for my $entry ( keys %lookup ) {
my %entry = %{ $lookup{$entry} };
print "#entry{keys %entry}\n"
}
use YAML;
print Dump \%lookup;
Output:
item1{'date'} item1{'name'}
---
item1:
date: "item1{'date'}"
name: "item1{'name'}"

Answer 3

If you know what items, you are going to need and what order you'll need them in
for keys, then re parsing the key is of questionable value. I prefer to store
them in levels.
$hash{ $h->{name} }{ $h->{date} } = $h;
# ... OR ...
$hash{ $h->{date} }{ $h->{name} } = $h;
foreach my $name ( sort keys %hash ) {
my $name_hash = $hash{$name};
foreach my $date ( keys %$name_hash ) {
print "\$hash{$name}{$date} => " . Dumper( $name_hash->{$date} ) . "\n";
}
}
For arbitrary levels, you may want a traversal function
sub traverse_hash (&#) {
my ( $block, $hash_ref, $path ) = #_;
$path = [] unless $path;
my ( #res, #results );
my $want = wantarray;
my $want_something = defined $want;
foreach my $key ( %$hash_ref ) {
my $l_path = [ #$path, $key ];
my $value = $hash_ref->{$key};
if ( ref( $value ) eq 'HASH' ) {
#res = traverse_hash( $block, $value, $l_path );
push #results, #res if $want_something && #res;
}
elsif ( $want_something ) {
#res = $block->( $l_path, $value );
push #results, #res if #res;
}
else {
$block->( $path, $value );
}
}
return unless $want_something;
return $want ? #results : { #results };
}
So this does the same thing as above:
traverse_hash {
my ( $key_path, $value ) = #_;
print( '$hash{' . join( '}{', #$key_path ) . '} => ' . ref Dumper( $value ));
();
} \%hash
;

Answer 4

Perl Solution
#!/usr/bin/perl -w
use strict;
use Data::Dumper;
sub main{
my %hash;
my #keys = qw(firstname lastname age); # hash's keys
# fname lname age
# --------|--------|-----
my #arr = ( [ 'foo1', 'bar1', '1' ],
[ 'foo2', 'bar2', '2' ],
[ 'foo3', 'bar3', '3' ]
);
# test if array set up correctly
print "\$arr[1][1] : $arr[1][1] \n"; # bar2
# loads the multidimensional array into the hash
for my $row (0..$#arr){
for my $col ( 0..$#{$arr[$row]} ){
my $itemnum = "item" . ($row+1); # using the item# format you used
$hash{$itemnum}->{$keys[$col]} = $arr[$row][$col];
}
}
# manually add a 4th item
$hash{item4} = {"firstname", "foo", "lastname", "bar", "age", "35"};
# How to Retrieve
# -----------------------
# single item pull
print "item1->firstname : $hash{item1}->{firstname} \n"; # foo1
print "item3->age : $hash{item3}->{age} \n"; # 3
# whole line 1
{ local $, = " ";
print "full line :" , %{$hash{item2}} , "\n"; # firstname foo2 lastname bar2 age 2
}
# whole line 2
foreach my $key (sort keys %{$hash{item2}}){
print "$key : $hash{item2}{$key} \n";
}
# Clearer description
#print "Hash:\n", Dumper %hash;
}
main();
This should be used in addition to the accepted answer. Your question was a little vague on the array to hash requirement, perhaps this is the model you are looking for?