agrep                  package:base                  R Documentation

Approximate String Matching (Fuzzy Matching)

Description:

     Searches for approximate matches to 'pattern' (the first argument)
     within the string 'x' (the second argument) using the Levenshtein
     edit distance.

Usage:

     agrep(pattern, x, ignore.case = FALSE, value = FALSE,
           max.distance = 0.1, useBytes = FALSE)

Arguments:

 pattern: a non-empty character string to be matched (_not_ a regular
          expression!).  Coerced by 'as.character' to a string if
          possible.

       x: character vector where matches are sought.  Coerced by
          'as.character' to a character vector if possible.

ignore.case: if 'FALSE', the pattern matching is _case sensitive_ and
          if 'TRUE', case is ignored during matching.

   value: if 'FALSE', a vector containing the (integer) indices of the
          matches determined is returned and if 'TRUE', a vector
          containing the matching elements themselves is returned.

max.distance: Maximum distance allowed for a match.  Expressed either
          as integer, or as a fraction of the _pattern_ length (will be
          replaced by the smallest integer not less than the
          corresponding fraction of the pattern length), or a list with
          possible components

          'all': maximal (overall) distance

          'insertions': maximum number/fraction of insertions

          'deletions': maximum number/fraction of deletions

          'substitutions': maximum number/fraction of substitutions

          If 'all' is missing, it is set to 10%, the other components
          default to 'all'.  The component names can be abbreviated. 

useBytes: logical. in a multibyte locale, should the comparison be
          character-by-chracter (the default) or byte-by-byte.

Details:

     The Levenshtein edit distance is used as measure of
     approximateness: it is the total number of insertions, deletions
     and substitutions required to transform one string into another.

     The function is a simple interface to the 'apse' library developed
     by Jarkko Hietaniemi (also used in the Perl String::Approx
     module), modified to work with multibyte character sets.  To save
     space it only supports the first 65536 characters of UTF-8 (where
     all the characters for human languages lie).  Note that it can be
     quite slow in UTF-8, and 'useBytes = TRUE' will be much faster.

Value:

     Either a vector giving the indices of the elements that yielded a
     match, or, if 'value' is 'TRUE', the matched elements (after
     coercion, preserving names but no other attributes).

Author(s):

     Original version by David Meyer, based on C code by Jarkko
     Hietaniemi.

See Also:

     'grep'

Examples:

     agrep("lasy", "1 lazy 2")
     agrep("lasy", c(" 1 lazy 2", "1 lasy 2"), max = list(sub = 0))
     agrep("laysy", c("1 lazy", "1", "1 LAZY"), max = 2)
     agrep("laysy", c("1 lazy", "1", "1 LAZY"), max = 2, value = TRUE)
     agrep("laysy", c("1 lazy", "1", "1 LAZY"), max = 2, ignore.case = TRUE)

