NAME

Text::Util::Chinese - A collection of subroutines for processing Chinese Text

DESCRIPTIONS

The subroutines provided by this module are for processing Chinese text. Conventionally, all input strings are assumed to be wide-characters. No `decode_utf8` or `utf8::decode` were done in this module. Users of this module should deal with input-decoding first before passing values to these subroutines.

Given the fact that corpus files are usually large, it may be a good idea to avoid slurping the entire input stream. Conventionally, subroutines in this modules accept "input iterator" as its way to receive a small piece of corpus at a time. The "input iterator" is a CodeRef that returns a string every time it is called, or undef if there are nothing more to be processed. Here's a trivial example to open a file as an input iterator:

    sub open_as_iterator {
        my ($path) = @_
        open my $fh, '<', $path;
        return sub {
            my $line = <$fh>;
            return undef unless defined($line);
            return decode_utf8($line);
        }
    }

    my $input_iter = open_as_iterator("/data/corpus.txt");

This $input_iter can be then passed as arguments to different subroutines.

Although in the rest of this document, `Iter` is used as a Type notation for iterators. It is the same as a CODE reference.

EXPORTED SUBROUTINES

word_iterator( $input_iter ) #=> Iter

This extracts words from Chinese text. A word in Chinese text is a token with N charaters. These N characters is often used together in the input and therefore should be a meaningful unit.

The input parameter is a iterator -- a subroutine that must return a string of Chinese text each time it is invoked. Or, when the input is exhausted, it must return undef. For example:

    open my $fh, '<', 'book.txt';
    my $word_iter = word_iterator(
        sub {
            my $x = <$fh>;
            return decode_utf8 $x;
        });

The type of return value is Iter (CODE ref).

extract_words( $input_iter ) #=> ArrayRef[Str]

This does the same thing as word_iterator, but retruns the exhausted list instead of iterator.

For example:

    open my $fh, '<', 'book.txt';
    my $words = extract_words(
        sub {
            my $x = <$fh>;
            return decode_utf8 $x;
        });

The type of return value is ArrayRef[Str].

It is likely that this subroutine returns an empty ArrayRef with no contents. It is only useful when the volume of input is a leats a few thousands of characters. The more, the better.

presuf_iterator( $input_iter, $opts) #=> Iter

This subroutine extract meaningful tokens that are prefix or suffix of input.

The 2nd argument $opts is a HashRef with parameters threshold and lengths. threshold should be an Int, lengths should be an ArrayRef[Int] and that constraints the lengths of prefixes and suffixes to be extracted.

The default value for threshold is 9, while the default value for lengths is [2,3]

extract_presuf( $input_iter, $opts ) #=> ArrayRef[Str]

Similar to presuf_iterator, but returns a ArrayRef[Str] instead.

sentence_iterator( $input_iter ) #=> Iter

This subroutine split input into sentences. It takes an text iterator, and returns another one.

phrase_iterator( $input_iter ) #=> Iter

This subroutine split input into smallelr phrases. It takes an text iterator, and returns another one.

tokenize_by_script( $text ) #=> Array[ Str ]

This subroutine split text into tokens, where each token is the same writing script.

looks_like_simplified_chinese( $text ) #=> Bool

This subroutine does a naive test on the input $text and returns true if $text looks like it is written in Simplified Chinese.

AUTHOR

Kang-min Liu <gugod@gugod.org>

LICENSE

Unlicense https://unlicense.org/