PERL/C2/Hash-in-Perl/English-timed
From Script | Spoken-Tutorial
| 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. |
| 09:42 | The Spoken Tutorial Project team: Conducts workshops using spoken tutorials. |
| 09:49 | Gives certificates to those who pass an online test. |
| 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. |
