Question

I am able to create a matrix using this code

#!/usr/bin/perl -w

@arr1 = (10,20,30);
@arr2 = (10,20,30);
@arr3 = (10,20,30);
@ref_arr = (\@arr1, \@arr2, \@arr3);

print"Prog starts\n";          

foreach $ref (@ref_arr) {
  #print @$ref->[0];
  foreach $val (@$ref) { 
    print "$val ";
  }
  print"\n";
}

Using the map function I can modify each value in the matrix like this

Example: increase every value by 1

foreach $ref (@ref_arr) {
  map($_++, @$ref);
} 

but I want to modify a certain row or a specific value, i.e. either add 1 to all of the second row’s values or to the first column of the second row

Answer 1

You must always use strict and use warnings at the top of every program that you write. This applies especially if you are asking for help with your code, as these measures will reveal simple errors that you would otherwise overlook

The map function is not for iterating over a list: it is for ‘mapping’ one list to another by applying a function to each element of the source list

When you write

map($_++,@$ref)

you are building and discarding a copy of the values in @list. What you should write is

$_++ for @$ref

As for how to modify a single value out of the array, your array initialisation can be simplified to

my @data = (
    [10, 20, 30], 
    [10, 20, 30], 
    [10, 20, 30]
)

I hope from this it is easier to see that the first 10 in the structure is accessible as $data[0][0] and, say, the last 20 is $data[2][1] (remembering that Perl arrays are indexed from zero). You can access and modifiy these values just as any ordinary scalar

As for your particular examples, the second row is @{$data[1]} so you can increment every element of the row by writing $_++ for @{$data[1]}. The first column of the second row is incremented with $data[1][0]++