Difference between revisions of "Linux-AWK/C2/MultiDimensional-Array-in-awk/English"

• Create multidimensional array in awk
• and scan the multidimensional array

We will do this through some examples.

System requirement

• Ubuntu Linux 16.04 OS and
• gedit text editor 3.20.1

You can use any text editor of your choice.

pre-requisite

You should have some basic knowledge of any programming language like C or C++.

If not, then please go through the corresponding tutorials on our website.

Please download and extract them.

We know that in single dimensional arrays, an array element is identified by a single index.

For example, array week is identified by a single index, day.

For example, a two dimensional array element is identified by a sequence of 2 indices.

with a separator between them.

The separator is the value of the built-in variable SUBSEP.

suppose we write multi[4,6]="value" in double quotes

Here multi is the name of multi-dimensional array.

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

Suppose,

the value of SUBSEP is hash symbol (#).

Then, those numbers are concatenated with a hash symbol (#) between them.

The default value of SUBSEP is the string within double quotes backslash 034.

It is actually a nonprinting character.

It will not appear usually in most input data.

Row 1 contains two elements A and B

Row 2 has two elements C and D

awk 'BEGIN{a[1,1]="A";a[1,2]="B";a[2,1]="C"; a[2,2]="D"}'

[Enter]

Type the command carefully as shown here.

Then press Enter.

So, the array is defined.

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

Let us add the print statement.

awk 'BEGIN{a[1,1]="A";a[1,2]="B";a[2,1]="C"; a[2,2]="D";print a[2,2]}'

[Enter]

And then type print space a (within square bracket) 2 comma 2

Press Enter to execute the command.

We can use in operator.

We have already seen it in single-dimensional array earlier in this series.

We have to write the entire sequence of indices within parentheses

and separated by commas.

Let us see this in an example

The same is available in the Code Files link of this tutorial.

a[1,1]="A";a[1,2]="B";a[2,1]="C"; a[2,2]="D"

if((3,1) in a)

Let us execute the file.

awk -f test_multi.awk

awk space hyphen small f space test_multi.awk and press Enter.

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

The transpose of a given matrix is formed by interchanging the rows and columns of a matrix.

How can we do this?

{

if (max_nf < NF)

max_nf = NF

max_nr = NR

for (x = 1; x <= NF; x++)

matrix[NR, x] = $x

}

max_nf = NF

And storing the calculated value in variable max_nf.

Value of NR is stored in max_nr variable.

When awk is processing the first record, max_nr will be equal to 1.

While processing second record, max_nr will be 2 and it continues this way.

When awk is processing last record, max_nr will store the total number of records.

for (x = 1; x <= NF; x++)

matrix[NR, x] = $x

Inside the for loop, we have iterator variable x.

x will traverse from one to NF, and x will be incremented by 1 after each iteration.

For every value of x, $x(dollar x) represents the value at field x.

That value will be stored in array matrix at index NR comma x.

For example, matrix of 1 comma 1 stores the value which is present at index 1 comma 1 from the input file.

{

if (max_nf < NF)

max_nf = NF

max_nr = NR

for (x = 1; x <= NF; x++)

matrix[NR, x] = $x

}

matrix array will be completely formed.

It will store entire data of input file in two dimensional array format.

END {

for (col = 1; col <= max_nf; col++) {

for (row = 1; row <= max_nr; row++)

printf("%s ", matrix[row, col])

printf("\n")

}

We have written a nested for loop to print the transpose of the matrix.

I assume your familiarity with basic C programming.

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

Pause the video here to look at the code in detail and understand on your own.

Awk does not have multi-dimensional array in the truest sense.

So, there cannot be any special for statement to scan the multidimensional array.

You can combine the for statement with the split function for this.

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

And place the various pieces into an array.

First argument contains the string to be chopped.

Second argument specifies the name of the array where split will put the chopped pieces into.

The first piece is stored in arr[1].

The second piece in arr[2] and so forth.

How can we do this?

The iterator will be set to each of the indices values for each iteration.

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

Let us execute the file.

[Enter]

awk space hyphen small f space multi_scan.awk

and press Enter.

Summary

In this tutorial we learnt to-

• Create a multidimensional array in awk
• and scan a multidimensional array

Assignment

• rotate a two dimensional array by 90 degree
• and print the rotated matrix.

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Acknowledgement

More information on this mission is available at

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And this is Praveen from IIT Bombay signing off.

Thank you for joining