Difference between revisions of "PERL/C2/Hash-in-Perl/English"

• Hash in Perl and
• Accessing element of a hash

• Ubuntu Linux12.04 operating system
• Perl 5.14.2 and
• gedit Text Editor

You can use any text editor of your choice.

Knowledge of comments, loops, conditional statements and Arrays will be an added advantage.

Please go through the relevant spoken tutorials on the spoken tutorial website.

• It's a key/value pair data structure
• Hash keys are unique
• However, Hash can have duplicate values

$hashName{'KeyName'}

dollar hashName open curly bracket single quote keyName single quote close curly bracket

#!/usr/bin/perl

%hash = (

'Name' => 'John',

'Department' => 'Finance'

);

print "Value of Key Name is: ", $hash{'Name'}, "\n";

<<pause>>

highlight keys 'Name' & 'Department'

highlight values 'John' & 'Finance'

$hash{'Name'}

These are the keys of hash.

And these are the values of hash.

Note: To access key of hash, one has to use dollar sign.

perl perlHash.pl

perl perlHash dot pl

and press Enter.

1. adding key is

dollar hashName open curly bracket

single quote KeyName single quote

close curly bracket equal to value semicolon

2. deleting key is

delete dollar hashName open curly bracket

single quote KeyName single quote

close curly bracket semicolon

use Data::Dumper;

#Hash of marks obtained in a subject

%hash = (

'Subject' => 'Math',

'Marks' => 98

);

print "Hash before adding keys\n";

print Dumper \%hash;

#Add Name and roll number of a student

$hash{'Name'} = 'Amol';

$hash{'RollNumber'} = 12;

print "Hash after addition of Name & RollNumber keys\n";

print Dumper \%hash;

delete $hash{'RollNumber'};

print "Hash after deletion of RollNumber key\n";

print Dumper \%hash;

We'll be adding, deleting the keys from this hash.

Here we are adding a key to an already created hash.

It is like assigning a value to a variable.

delete keyword is used to delete the key.

We need to pass the key to delete it.

perl hashKeyOperations.pl

perl hashKeyOperations dot pl

and press Enter.

<<pause>>

sort open bracket keys percentage hashName close bracket semicolon

Similarly, we can sort hash values as

sort open bracket values percentage hashName close bracket semicolon

Type the code as displayed on the screen in your sortHash dot pl file.

%addressHash = (

'City' => 'Pune',

'State' => 'Maharashtra',

'Country' => 'India'

);

foreach $key (sort(keys %addressHash)) {

print "Key: ", $key, " ==> ", $addressHash{$key}, "\n";

}

foreach $value (sort(values %addressHash)) {

print "Value: $value\n";

}

Here, to sort the keys we have used the sort inbuilt function, along with the keys function.

This will sort the hash keys in alphabetical order.

Similarly, we can use the sort function on values of hash.

Sorting can also be done on numeric keys and/or values.

perl sortHash.pl

perl sortHash dot pl

• keys function is used to retrive all the keys of hash
• values function returns values of all the keys whereas
• each function iterates over hash and returns key/value pair from hash

For this, we'll use perlHash dot pl script, which we have created earlier in this tutorial.

#!/usr/bin/perl

%hash = (

'Name' => 'John',

'Department' => 'Finance'

);

print "Value of Key Name is: ", $hash{'Name'}, "\n";

@keysOfHash = keys(%hash);

print "Keys of a Hash are: @keysOfHash\n";

@valuesOfHash = values(%hash);

print "Values of a Hash are: @valuesOfHash\n";

while (($key, $value) = each(%hash)) {

print "key: $key and value: $value\n";

}

<<pause>>

@keysOfHash = keys(%hash);

@valuesOfHash = values(%hash);

keys function on hash, returns an array which contains all keys of hash.

values function on hash returns an array of values for all keys of hash.

each function returns the key/value pair.

Here, we have used the while loop.

It will iterate over each key/value pair of hash, that is returned by each function.

perl perlHash.pl

perl perlHash dot pl

Press Enter

foreach $variable (keys(%hashName)) {

# Action to be performed

}

Then perform a set of actions on the value of a key.

Here, each iteration of foreach loop will assign key from hash to $variable.

Then it will use that $variable to fetch the value or to perform a set of actions.

# Action to be performed

}

So, let me switch to loopingOverHash dot pl in gedit.

%hash = (

'Name' => 'John',

'Department' => 'Finance'

);

foreach $key (keys(%hash)) {

print "Key is $key and it's value is $hash{$key}\n";

}

print "==================

====================\n";

foreach $value (values(%hash)) {

print "Value is $value\n";

}

<<pause>>

foreach $key (keys(%hash))

Here in our case,

1st time dollar key ($key) contains the Department as key.

In the next iteration of foreach, Name key is returned.

So, keys returned will not be in the sequence defined at the time of creating hash.

foreach $value (values(%hash))

perl loopingOverHash.pl

perl loopingOverHash dot pl

and press Enter.

<pause>

In this tutorial, we learnt -

• Hash in Perl and
• Accessing elements of a hash
• using sample programs.

1. Declare hash having student name as key
2. And his/her percentage as the value.
3. Loop over hash using keys, values and each function
4. Then print the percentage of each student.

It summaries the Spoken Tutorial project

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Gives certificates to those who pass an online

test

For more details, please write to

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http://spoken-tutorial.org\NMEICT-Intro

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This is Amol Brahmankar signing off.

Thanks for joining