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;

1. Insert an item $V with a key $K?

   $hash{$K} = $V

2. 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" 
    }

3. Delete a particular name / key?

   delete $hash{$K}

4. 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"}