Sandhya.np14 at 15:23, 10 July 2019

2019-07-10T15:23:38Z

PoojaMoolya: Created page with " {| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Hello and Welcome to the spoken tutorial on creating '''multidimensional arrays'''..."

2018-12-14T06:38:11Z

Created page with " {| border=1 | <center>'''Time'''</center> | <center>'''Narration'''</center> |- | 00:01 | Hello and Welcome to the spoken tutorial on creating '''multidimensional arrays'''..."

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{| border=1
| <center>'''Time'''</center>
| <center>'''Narration'''</center>

|-
| 00:01
| Hello and Welcome to the spoken tutorial on creating '''multidimensional arrays''' in '''awk'''.

|-
| 00:07
| In this tutorial we will learn to- Create '''multidimensional array '''in '''awk''' and scan the '''multidimensional array'''

|-
|00:18
|We will do this through some examples.

|-
|00:21
| To record this tutorial, I am using '''Ubuntu Linux 16.04 Operating System '''and''' ''' '''gedit text editor 3.20.1'''

|-
|00:33
|You can use any text editor of your choice.

|-
| 00:37
| To practice this tutorial, you should have gone through previous '''awk''' tutorials on '''array''' on this website.

|-
|00:45
|You should have some basic knowledge of any programming language like '''C''' or '''C++'''.

|-
|00:52
|If not, then please go through the corresponding tutorials on our website.

|-
|00:58
| The files used in this tutorial are available in the '''Code Files''' link on this tutorial page.

Please download and extract them.

|-
| 01:08
| What is a '''multidimensional array '''in '''awk'''?

|-
|01:12
|We know that in '''single dimensional arrays, '''an '''array element '''is identified by a single '''index'''.

|-
|01:19
|For example, '''array week '''is identified by a single '''index, day'''.

|-
| 01:26
| However, in '''multidimensional array''', an '''element '''is identified by a sequence of multiple '''indices.'''

|-
|01:34
|For example, a '''two dimensional array element '''is identified by a sequence of '''2 indices'''.

|-
| 01:42
| Here, '''multiple indices '''are concatenated into a single '''string''', with a '''separator '''between them.

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|01:50
|The '''separator''' is the value of the '''built-in variable SUBSEP'''.

|-
| 01:55
| The combined '''string''' is used as a single '''index''' for a simple '''one dimensional array'''.

|-
| 02:01
| For example, Suppose we write '''multi within square brackets 4 comma 6 equal to value in double quotes'''

|-
|02:11
|Here '''multi '''is the name of '''multi-dimensional array. '''

Then, the numbers '''4 '''and''' 6 '''are converted to a '''string'''.

|-
|02:21
|Suppose, the value of '''SUBSEP''' is '''hash symbol (#).'''

|-
| 02:26
|Then, those numbers are concatenated with a '''hash symbol (#)''' between them.

|-
| 02:32
| So, the '''array element multi within square brackets within double quotes 4 hash 6 '''is set to '''value within double quotes.'''

|-
|02:43
|The default value of '''SUBSEP''' is the '''string within double quotes backslash 034'''.

|-
|02:50
|It is actually a '''nonprinting character. '''

It will not appear usually in most input data.

|-
| 02:58
| Let us try to declare a '''two dimensional array '''as shown in the slide.

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|03:03
|Row 1 contains two '''elements A '''and '''B'''

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| 03:08
|Row 2 has '''two elements C '''and '''D'''

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| 03:12
| Open the '''terminal''' by pressing '''Ctrl''', '''Alt''' and '''T''' keys

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| 03:17
| Go to the folder in which you downloaded and extracted the '''Code Files''' using '''cd command'''

|-
| 03:24
| Now define the '''array '''as follows. Type the command carefully as shown here.

Then press '''Enter.'''

|-
|03:35
| We get a''' command prompt''' back without any '''error'''.

So, the '''array''' is defined.

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|03:41
| We do not get any output because we have not given anything to print in the code.

|-
| 03:47
|Let us add the '''print statement'''.

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|03:50
| Press the Up arrow key to get the previously executed command in the '''terminal'''.

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| 03:56
| Just before the closing '''curly bracket''', type '''semicolon''' space '''print space a within square brackets 2 comma 2'''

Press '''Enter''' to execute the command.

|-
|04:13
| Notice, we get the output as '''capital D.'''

|-
| 04:18
| How to test if a particular '''index sequence '''exists in a given '''multidimensional array'''?

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|04:25
| We can use '''in operator.'''

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|04:28
| We have already seen it in '''single-dimensional array '''earlier in this series.

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|04:34
| We have to write the entire '''sequence '''of '''indices '''within '''parentheses ''' and separated by '''commas'''.

|-
|04:42
| Let us see this in an example.

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| 04:45
| I have already written a script named '''test_multi.awk'''

|-
|04:51
| The same is available in the '''Code Files''' link of this tutorial page.

|-
| 04:56
| I have defined a '''2 by 2 array '''as seen in our previous discussion.

|-
| 05:02
| Then I have written two '''if conditions'''.

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| 05:06
| The first '''if condition '''checks whether the '''element '''at the '''index one comma one, '''is present or not.

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| 05:13
| We have to write the '''index '''for '''multidimensional array '''within '''parentheses'''.

|-
| 05:18
| If the '''condition '''is '''true''', it will print '''one comma one is present'''.

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|05:23
| Else it will print '''one comma one is absent.'''

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|05:28
| Similarly, we will check for the presence of the '''element '''at '''index three comma one.'''

Let us execute the file.

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| 05:36
| Switch to the '''terminal '''and type '''awk space hyphen small f space test underscore multi dot awk '''and press '''Enter.'''

|-
| 05:49
| The output says '''one comma one is present '''and '''three comma one is absent.'''

|-
| 05:55
| Let us take one more example.

Say, we want to create the '''transpose '''of a '''matrix'''.

|-
|06:02
| The '''transpose''' of a given '''matrix''' is formed by interchanging the '''rows '''and '''columns '''of a '''matrix'''.

How can we do this?

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| 06:11
| I have created a '''two-dimensional array matrix '''in the file '''2D-array.txt.'''

|-
|06:19
| I have written a code named '''transpose.awk'''

|-
| 06:24
| First look at the '''action section''' of this '''awk script.'''

|-
| 06:29
| Here we are calculating the maximum number of '''fields''' in a '''row'''.

And stored the calculated value in the '''variable max_nf.'''

|-
| 06:40
| As we know, '''NR '''is the number of current '''records '''processed by '''awk'''.

Value of '''NR '''is stored in '''max_nr variable.'''

|-
| 06:50
| '''Awk '''will process the''' input file''' from the first '''record '''to the last '''record'''.

|-
| 06:56
|When '''awk '''is processing the first '''record''', '''max_nr '''will be equal to '''1'''.

|-
| 07:03
|While processing second '''record''', '''max_nr '''will be '''2 '''and it continues this way.

|-
| 07:11
|When '''awk '''is processing last '''record, max_nr '''will store the total number of '''records'''.

|-
| 07:19
| Now we should read the data from '''input file '''and store the data into a '''two dimensional array'''.

|-
| 07:26
|Inside the '''for loop, '''we have '''iterator variable x.'''

|-
| 07:31
|'''x '''will traverse from one to '''NF''', and '''x '''will be incremented by 1 after each '''iteration'''.

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| 07:39
|For every value of '''x, $x(dollar x) '''represents the value at '''field x.'''

|-
| 07:46
|That value will be stored in '''array matrix '''at '''index NR comma x.'''

|-
| 07:53
|For example, '''matrix of 1 comma 1 '''stores the value which is present at '''index 1 comma 1 '''from the '''input file.'''

|-
| 08:02
| So, after '''awk '''has processed the entire '''input file '''with this code, '''matrix array '''will be completely formed.

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| 08:10
|It will store entire data of '''input file '''into a '''two dimensional array''' format.

|-
| 08:16
| Now, let’s us look inside the '''END section. '''

|-
| 08:20
|We have written a '''nested for loop '''to print the '''transpose '''of the '''matrix'''.

|-
| 08:25
|I assume your familiarity with basic '''C programming'''.

So, I am not explaining this portion of code in detail.

|-
| 08:34
|Pause the video here to look at the code in detail and understand on your own.

|-
| 08:40
| Now, we will learn how to scan a '''multidimensional array.'''

|-
| 08:45
|'''Awk''' does not have a '''multi-dimensional array''' in the truest sense.

|-
| 08:50
|So, there cannot be any special '''for statement '''to scan the '''multidimensional array. '''

|-
| 08:56
| You can have '''multidimensional '''way to scan an '''array.'''

|-
| 09:00
|You can combine the '''for statement '''with the '''split function '''for this.

|-
| 09:05
| Let us see what the '''split function''' is.

'''split function''' is used to chop up or split a '''string''' into pieces.

|-
| 09:14
|And place the various pieces into an '''array'''.

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| 09:18
| The syntax is as follows. First '''argument''' contains the '''string''' to be chopped.

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| 09:25
|Second '''argument '''specifies the name of the '''array '''where '''split '''will put the chopped pieces into.

|-
| 09:33
| The third '''argument '''mentions the '''separator '''that will be used to chop the '''string''' up.

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| 09:39
|The first piece is stored in ''' arr 1'''.

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| 09:43
|The second piece in '''arr 2''' and so forth.

|-
| 09:48
| Suppose, we want to recover the original sequence of '''indices''' from an already created '''array'''.

How can we do this?

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| 09:56
| I have written a code named '''multi_scan.awk'''

|-
| 10:02
| Entire code is written inside the '''BEGIN section'''.

|-
| 10:06
| First we have created an '''array '''named '''a '''and assigned these values to it.

|-
| 10:12
| Then we have the '''for loop '''with an '''iterator'''.

|-
| 10:16
|The '''iterator '''will be set to each of the '''indices values '''for each '''iteration'''.

Say '''1,1''' then '''1,2 '''and so on.

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| 10:27
| The '''split function '''breaks the '''iterator '''into pieces separated by '''SUBSEP.'''

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| 10:34
| The pieces will be stored in the '''array arr.'''

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| 10:38
| So, '''arr[1] '''and '''arr[2] '''will contain the first '''index '''and second '''index '''respectively.

Let us execute this file.

|-
| 10:48
| Switch to the '''terminal '''and type- '''awk space hyphen small f space multi underscore scan dot awk '''

and press '''Enter.'''

|-
| 11:01
| See the output; the original sequence of '''indices '''are recovered.

|-
| 11:07
| Let us summarize. In this tutorial we learnt to- Create a '''multidimensional array '''in '''awk''' and scan a '''multidimensional array'''

|-
| 11:18
| As an assignment, write an '''awk script '''to rotate a '''two dimensional array '''by 90 degree and print the rotated '''matrix'''.

|-
| 11:28
| The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.

|-
| 11:36
| The '''Spoken Tutorial Project''' team conducts workshops using spoken tutorials.

And gives certificates on passing online tests.

|-
| 11:45
|For more details, please write to us.

|-
| 11:49
| Please post your timed queries in this forum.

|-
|11:53
| Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at this link.

|-
| 12:05
| The script has been contributed by Antara. And this is Praveen from IIT Bombay signing off.

Thank you for joining

|}

Linux-AWK/C2/MultiDimensional-Array-in-awk/English-timed - Revision history

Sandhya.np14 at 15:23, 10 July 2019

PoojaMoolya: Created page with " {| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Hello and Welcome to the spoken tutorial on creating '''multidimensional arrays'''..."