about_search_coll: Locale-Sensitive Text Searching in stringi


String searching facilities described here provide a way to locate a specific piece of text. Interestingly, locale-sensitive searching, especially on a non-English text, is a much more complex process than it seems at the first glance.

Locale-Aware String Search Engine

All stri_*_coll functions in stringi use ICU’s StringSearch engine, which implements a locale-sensitive string search algorithm. The matches are defined by using the notion of “canonical equivalence” between strings.

Tuning the Collator’s parameters allows you to perform correct matching that properly takes into account accented letters, conjoined letters, ignorable punctuation and letter case.

For more information on ICU’s Collator and the search engine and how to tune it up in stringi, refer to stri_opts_collator.

Please note that ICU’s StringSearch-based functions are often much slower that those to perform fixed pattern searches.


Marek Gagolewski and other contributors


ICU String Search Service – ICU User Guide, https://unicode-org.github.io/icu/userguide/collation/string-search.html

L. Werner, Efficient Text Searching in Java, 1999, https://icu-project.org/docs/papers/efficient_text_searching_in_java.html