Perl Weekly Challenge 110: Mangling Text Files

One way to let me improve my knowledge about Raku (aka Perl 6) is to implement programs in it. Unluckily, I don’t have any production code to implement in Raku yet (sob!). So, why not try solving the Perl Weekly Challenge tasks?

In the following, the assigned tasks for Challenge 110.

PWC 110 - Task 1

In the first task I have to select a few valid phone numbers depending on some specifications.
This task could be easily solved with a bunch of regular expressions, used to validate every line in input. I decided to place the regular expressions into an array, so that I can use a junction to quickly test on a single line if the input matches any of the regular expression, and if so, I do print the matching line on standard output.
The code is therefore the following:

sub MAIN( Str $file-name = 'phone.txt' ) {
    my @regexps = rx / ^ \s* <[+]> \d ** 2 \s+ \d ** 10 $ /
                , rx / ^ \s* <[(]> \d ** 2 <[)]> \s+ \d ** 10 $ /
                , rx / ^ \s* \d ** 4 \s+ \d ** 10 $ /;

    $_.say if $_ ~~ any @regexps for $file-name.IO.lines;

As you can see, the main idea is to iterate on every file lines, than smart match against any of the defined regular expressions.
However, this can be done better, even without defining a grammar, so I decided to put togethere the parts of the same regular expressions. For example, the length of the phone number is always the same, so I produced two different regular expression: the first to match the number, the second to match any of the prefix.
Therefore, I had to smart match only against a combination of the two:

sub MAIN( Str $file-name = 'phone.txt' ) {
    my $phone-regexp  = rx/ \d ** 10 /;
    my $prefix-regexp = rx/
             <[+]> \d ** 2
             || <[(]> \d ** 2 <[)]>
             || \d ** 4

    my $phone-rx = rx / ^ \s* $prefix-regexp \s+ $phone-regexp $ /;
    $_.say if $_ ~~ $phone-rx for $file-name.IO.lines;

PWC 110 - Task 2

The second task was about transposing the content of a CSV-like text file.
In order to transpose every line, I decided to put the lines into an array, than to print out the array re-mapped in a columnar way.
My first implementation was quite trivial:

sub MAIN( Str $file-name = 'people.txt' ) {

    my @content;
    @content.push: .split( ',' ) for $file-name.IO.lines;

    for 0 ..^ @content[ 0 ].elems -> $column {
        my @row.push:  @content[ $_ ][ $column ] for 0 ..^ @content.elems;
        @row.join( ',' ).say;

The main part is the for loop, where I iterate on every column (assuming @content[ 0 ] contains the exact number of columns that are in all the other rows), and I push the content of every row at that column in another array named @row, that is then printed out.
But this is too much code, so I used the map function to do what the for loop does:

sub MAIN( Str $file-name = 'people.txt' ) {

    my @content;
    @content.push: .split( ',' ) for $file-name.IO.lines;

    my @transposed.push: *[ $_ ] for 0 ..^ @content[ 0 ].elems;
    $_.join( ',' ).say for @transposed;


The map iterates on every line, and on every line it does extract the current column by means of an inner for loop, then the result is placed into @transposed array that is then printed one line at a time.

The article Perl Weekly Challenge 110: Mangling Text Files has been posted by Luca Ferrari on April 26, 2021