📘 Removing duplicated words using Perl 6

📘 Removing duplicated words using Raku

N. B. Perl 6 has been renamed to Raku. Click to read more.

Remove repeated words from froma sentence.

Repeated words are most often unintended typing mistakes. In rare cases, though, this is correct like with the word that:

He said that that tree is bigger

Anyway, let us remove the double words ignoring the grammar for now. To find if the word is repeated, a regex with variables can be used. Then, using a substitution, only one copy of a word is passed to the resulting string.

my $string = 'This is is a string';
$string ~~ s:g/ << (\w+) >> ' ' << $0 >> /$0/;

say $string;

The regex part of the sroutine is a regex that is first looking for a word (as a sequence of word characters \w+) and its copy after a space. The first occurrence is saved in the $0 variable, which is immediately used in the same regex. It is also used in the replacement part.

To prevent repetitions, the word-edge anchors are used: << for the beginning of a word and >> for its end. In the given example, this prevents treating the last two letters of the word This as a separate word, is, and thus, the correct phrase This is a string will not be broken after the substitution.

Notice that non-literal spaces in a regex are not taking part in string matching, although, they are necessary in a sequence << (\w+) >>. The construction <<(\w+)>> is a syntax error as it is similar to the character class <[...]> or a reference to a named regex like <:alnum>, and the compiler prefers explicit spaces in this case.

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