agrep {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-character (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.

How complex a match may be found can depend on the size of integers. As from R 2.9.2 this uses 64-bit integers where available (even on 32-bit platforms) to try to be consistent across platforms.

### 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)

[Package base version 2.9.2 Index]