PERL/C2/Hash-in-Perl/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Hash in PERL.
00:05	In this tutorial, we will learn about:
00:09	Hash in PERL and
00:11	accessing an element of a hash.
00:14	For this tutorial, I am using:
00:16	Ubuntu Linux 12.04 operating system
00:21	Perl 5.14.2 and
00:24	gedit Text Editor.
00:26	You can use any text editor of your choice.
00:30	To practice this tutorial, you should have knowledge of variables & data Structures in PERL.
00:38	Knowledge of comments, loops, conditional statements and arrays will be an added advantage.
00:46	Please go through the relevant spoken tutorials on the Spoken Tutorial website.
00:52	Hash is an unordered collection of data.
00:56	It's a key/value pair data structure.
00:59	Hash keys are unique.
01:01	However, Hash can have duplicate values.
01:05	This is the declaration of a hash.
01:08	Let us see how to get the value of a key from hash.
01:12	The syntax for accessing the value of a key is:
01:17	dollar hashName open curly bracket single quote keyName single quote close curly bracket.
01:26	Let us understand hash using a sample program.
01:31	I have already typed the code in perlHash dot pl file in gedit.
01:37	Type the code as shown in your perlHash dot pl file.
01:42	Hash in PERL is declared with percentage sign (%).
01:47	These are the keys of hash
01:49	and these are the values of hash.
01:53	Note: To access key of a hash, one has to use dollar sign.
01:59	Press Ctrl + S to save the file.
02:02	Then switch to terminal and execute the Perl script as:
02:08	perl perlHash dot pl
02:11	and press Enter.
02:14	The output is as shown on the terminal.
02:19	Now, let us see add and delete of keys from hash.
02:24	The syntax for:
02:26	Adding key is- dollar hashName open curly bracket
02:30	single quote KeyName single quote
02:34	close curly bracket equal to $value semicolon.
02:40	Deleting key is- delete dollar hashName open curly bracket
02:46	single quote KeyName single quote close curly bracket semicolon.
02:53	Now, let us understand this using a sample program.
02:58	I have already typed the code in hashKeyOperations dot pl file.
03:05	This is the declaration of a hash.
03:08	We will be adding, deleting the keys from this hash.
03:13	Here we are adding a key to an already created hash.
03:18	It is like assigning a value to a variable.
03:23	delete keyword is used to delete the key.
03:27	We need to pass the key to delete it.
03:31	Press Ctrl+S to save the file.
03:35	Switch to the terminal and execute the Perl script as:
03:40	perl hashKeyOperations dot pl
03:44	and press Enter.
03:47	Output will be as shown on the terminal.
03:52	Let us look at sorting of hash keys and values.
03:57	Syntax to sort keys is:
04:00	sort open bracket keys percentage hashName close bracket semicolon.
04:07	Similarly, we can sort hash values as:
04:11	sort open bracket values percentage hashName close bracket semicolon.
04:18	Let us understand sorting functionality using a sample program.
04:24	Let me switch to sortHash dot pl on gedit.
04:30	Type the code as displayed on the screen, in your sortHash dot pl file.
04:36	Here, we have declared hash of address.
04:41	Here, to sort the keys, we have used the sort inbuilt function along with the keys function.
04:49	This will sort the hash keys in alphabetical order.
04:54	Similarly, we can use the sort function on values of hash.
04:59	Sorting can also be done on numeric keys and/or values.
05:05	Save the file and switch to terminal.
05:09	Execute the script by typing perl sortHash dot pl and press Enter.
05:17	The output will be as shown on the terminal.
05:22	Now, let us see how to get all keys and values of a hash.
05:27	PERL provides inbuilt function to fetch all the hash keys and values.
05:34	keys() function is used to retrieve all the keys of a hash,
05:40	values() function returns values of all the keys whereas
05:46	each() function iterates over hash and returns key/value pair from hash.
05:53	Let us understand these using a sample program.
05:57	For this, we'll use perlHash dot pl script which we have created earlier in this tutorial.
06:07	Type the following piece of code as shown on the screen.
06:12	Let us understand the code now.
06:15	keys() function on hash returns an array which contains all keys of hash.
06:22	values() function on hash returns an array of values for all keys of hash.
06:30	each() function returns the key/value pair.
06:34	Here, we have used the while loop.
06:36	It will iterate over each key/value pair of hash that is returned by each function.
06:43	Press Ctrl+S to save the file.
06:48	Now, let us execute the script on the terminal by typing
06:53	'perl perlHash dot pl'
06:58	and press Enter.
07:01	The following output will be seen on the terminal.
07:05	Now, let us see few other ways of looping over hash.
07:10	We can use foreach loop to iterate over each key of hash.
07:15	Then perform a set of actions on the value of key.
07:20	The syntax is as displayed on the screen.
07:24	Here, each iteration of foreach loop will assign key from hash to $variable.
07:32	Then, it will use that $variable to fetch the value or to perform a set of actions.
07:40	Similarly, we can loop over hash values as shown on the screen.
07:47	We will look at sample program.
07:49	So, let me switch to loopingOverHash dot pl in gedit.
07:55	Type the following piece of code as shown in your loopingOverHash dot pl.
08:02	This piece of code returns single key of hash.
08:07	Here, in our case,
08:09	1st time dollar key ($key) contains the Department as key.
08:15	In the next iteration of foreach, Name key is returned.
08:21	Note: Hash is an unordered collection of data.
08:26	So, keys returned will not be in the sequence defined at the time of creating hash.
08:33	The loop on values works in a similar way.
08:38	Press Ctrl + S to save the file.
08:41	Then, switch to terminal and execute the Perl script as:
08:46	perl loopingOverHash dot pl
08:50	and press Enter.
08:53	The following output is displayed on the terminal.
08:58	Let us summarize. In this tutorial, we learnt:
09:01	Hash in PERL and
09:03	accessing elements of a hash
09:05	using sample programs.
09:08	Here is an assignment for you:
09:11	Declare hash having student name as key
09:15	and his/her percentage as the value.
09:18	Loop over hash using keys(), values() and each() function.
09:24	Then print the percentage of each student.
09:29	Watch the video available at the following link.
09:32	It summarizes the Spoken Tutorial project.
09:37	If you do not have good bandwidth, you can download and watch it.
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09:53	For more details, please write to: contact at spoken hyphen tutorial dot org.
10:02	Spoken Tutorial project is a part of the "Talk to a Teacher" project.
10:06	It is supported by the National Mission on Education through ICT, MHRD, Government of India.
10:15	More information on this mission is available at: spoken hyphen tutorial dot org slash NMEICT hyphen Intro.
10:26	Hope you enjoyed this PERL tutorial.
10:30	This is Amol, signing off.
10:33	Thanks for joining.

Contributors and Content Editors

Gaurav, Nancyvarkey, PoojaMoolya, Sandhya.np14