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String Functions

This module contains functions for string operations and computations.

Conventions

All functions and errors in this module and errors are assigned to the http://basex.org/modules/string namespace, which is statically bound to the string prefix.

Computations

string:levenshtein

Signature
string:levenshtein(
  $value1  as xs:string,
  $value2  as xs:string
) as xs:double
SummaryComputes the Damerau-Levenshtein Distance for $value1 and $value2 and returns a normalized double value (0 – 1). The returned value is computed as follows:
  • 1 – distance / max(lengths of strings)
  • 1 is returned if the strings are equal; 0 is returned if the strings are too different.
Errors
boundsThe specified string exceeds the maximum supported length.
Examples
string:levenshtein("flower", "flowers")
Result: 0.8571428571428571e0
let $norm := ft:normalize(?, { 'stemming': true() })
return string:levenshtein($norm("HOUSES"), $norm("house"))
1 is returned after the input has been normalized (words are stemmed, converted to lower case, and diacritics are removed).

string:jaro-winkler

Signature
string:jaro-winkler(
  $value1  as xs:string,
  $value2  as xs:string
) as xs:double
SummaryComputes the Jaro-Winkler Distance for $value1 and $value2 and returns a double value (0 – 1). 1 is returned if the strings are equal; 0 is returned if the strings are too different.
Examples
string:jaro-winkler("flower", "flowers")
Result: 0.98e0
let $norm := ft:normalize(?, { 'stemming': true() })
return string:jaro-winkler($norm("HOUSES"), $norm("house"))
1 is returned after the input has been normalized (words are stemmed, converted to lower case, and diacritics are removed).

string:token-sort-ratio

Added: New function.

Signature
string:token-sort-ratio(
  $value1  as xs:string,
  $value2  as xs:string
) as xs:double
SummaryTokenizes $value1 and $value2 on whitespace, sorts the tokens, and returns the normalized string:levenshtein similarity (0 – 1) of the rejoined strings. As the tokens are sorted before the comparison, the measure is insensitive to their order. 1 is returned if the strings are equal after sorting; 0 is returned if they are too different.
Errors
boundsThe specified string exceeds the maximum supported length.
Examples
string:token-sort-ratio("Ishida Yūtei", "Yūtei Ishida")
Result: 1e0. 1 is returned, as both strings consist of the same tokens in a different order.

string:token-set-ratio

Added: New function.

Signature
string:token-set-ratio(
  $value1  as xs:string,
  $value2  as xs:string
) as xs:double
SummaryTokenizes $value1 and $value2 on whitespace and compares them as sets: the shared tokens and the tokens unique to either string are reassembled, compared with the normalized string:levenshtein similarity, and the best of the resulting values (0 – 1) is returned. A high value is returned if the tokens of one string are a subset of the other; this makes the measure robust against extra or omitted words.
Errors
boundsThe specified string exceeds the maximum supported length.
Examples
string:token-set-ratio("Fortuny y Marsal", "Fortuny Marsal")
Result: 1e0. 1 is returned, as the tokens of the second string are a subset of the first.

string:ngram-similarity

Added: New function.

Signature
string:ngram-similarity(
  $value1  as xs:string,
  $value2  as xs:string,
  $n       as xs:integer  := 2
) as xs:double
SummaryComputes the similarity of $value1 and $value2 via the Sørensen-Dice coefficient on the sets of their character n-grams of length $n, and returns a double value (0 – 1). 1 is returned if the n-gram sets are equal; 0 is returned if they are disjoint. The measure is robust against transliteration and OCR drift, where string:levenshtein thresholds tend to be brittle.
Errors
ngramThe specified n-gram length is not positive.
Examples
string:ngram-similarity("night", "nacht")
Result: 0.25e0
string:ngram-similarity("Massys", "Metsys")
Result: 0.4e0. The two name variants share 2 of 5 bigrams each.

string:ngrams

Added: New function.

Signature
string:ngrams(
  $value  as xs:string,
  $n      as xs:integer  := 2
) as xs:string*
SummaryReturns the character n-grams of length $n of $value, in string order and including duplicates. A non-empty string that is shorter than $n yields a single n-gram with the whole string; an empty string yields no n-grams. Whitespace is treated like any other character, and the input is not normalized. The distinct n-grams are the building block of string:ngram-similarity, which equals the Sørensen-Dice coefficient over distinct-values(string:ngrams(...)) of both arguments.
Errors
ngramThe specified n-gram length is not positive.
Examples
string:ngrams("flower")
Result: 'fl', 'lo', 'ow', 'we', 'er'
string:ngrams("flower", 3)
Result: 'flo', 'low', 'owe', 'wer'

string:soundex

Signature
string:soundex(
  $value  as xs:string
) as xs:string
SummaryComputes the Soundex value for the specified string $value. The algorithm can be used to find and index English words with similar pronouncation.
Examples
string:soundex("Michael")
Result: 'M240'
string:soundex("OBrien") = string:soundex("O'Brien")
Result: true()

string:cologne-phonetic

Signature
string:cologne-phonetic(
  $value  as xs:string
) as xs:string
SummaryComputes the Kölner Phonetik value for the specified string $value. Similar to Soundex, the algorithm is used to find similarly pronounced words, but for the German language. As the first returned digit can be 0, the result is returned as string.
Examples
string:cologne-phonetic("Michael")
Result: '645'
every $s in ("Mayr", "Maier", "Meier")
satisfies string:cologne-phonetic($s) = "67"
Result: true()

Formatting

string:format

Signature
string:format(
  $pattern    as xs:string,
  $values...  as item()
) as xs:string
SummaryReturns a formatted string. The remaining $values are incorported into the $pattern, according to Java’s printf syntax.
Errors
formatThe specified format is invalid.
Examples
string:format("%b", true())
Result: 'true'
string:format("%06d", 256)
Result: '000256'
string:format("%e", 1234.5678)
Result: '1.234568e+03'

Errors

CodeDescription
boundsThe specified string exceeds the maximum supported length.
formatThe specified format is invalid.
ngramThe specified n-gram length is not positive.

Changelog

Version 13.0Version 11.0Version 10.0
  • Updated: Renamed from Strings Module to String Module. The namespace URI has been updated as well.
  • Updated: string:format, string:cr, string:nl and string:tab adopted from the obsolete Output Module.
Version 8.3
  • Added: New module added. Functions were adopted from the obsolete Utility and Output Modules.
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String Functions