agrep: Approximate String Matching (Fuzzy Matching)

Description

Searches for approximate matches to pattern (the first argument) within each element of the string x (the second argument) using the generalized Levenshtein edit distance (the minimal possibly weighted number of insertions, deletions and substitutions needed to transform one string into another).

Usage

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

Arguments

pattern

a non-empty character string or a character string containing a regular expression (for fixed = FALSE) to be matched. Coerced by as.character to a string if possible.

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

max.distance

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

cost:: maximum number/fraction of match cost (generalized Levenshtein distance)
all:: maximal number/fraction of all transformations (insertions, deletions and substitutions)
insertions:: maximum number/fraction of insertions
deletions:: maximum number/fraction of deletions
substitutions:: maximum number/fraction of substitutions

If cost is not given, all defaults to 10%, and the other transformation number bounds default to all. The component names can be abbreviated.

costs

a numeric vector or list with names partially matching insertions, deletions and substitutions giving the respective costs for computing the generalized Levenshtein distance, or NULL (default) indicating using unit cost for all three possible transformations. Coerced to integer via as.integer 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.

fixed

logical. If TRUE (default), the pattern is matched literally (as is). Otherwise, it is matched as a regular expression.

useBytes

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

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).

Details

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

As from R 2.10.0 this uses tre by Ville Laurikari (http://http://laurikari.net/tre/), which supports MBCS character matching much better than the previous version.

The main effect of useBytes is to avoid errors/warnings about invalid inputs and spurious matches in multibyte locales. It inhibits the conversion of inputs with marked encodings, and is forced if any input is found which is marked as "bytes".

Examples

Run this code

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)