# agrep

##### Approximate String Matching (Fuzzy Matching)

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).

- Keywords
- character

##### Usage

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

##### 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.

This uses `tre`

by Ville Laurikari
(http://laurikari.net/tre/), which supports MBCS
character matching.

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"`

(see
`Encoding`

).

##### Value

`agrep`

returns 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).

`agrepl`

returns a logical vector.

##### Note

Since someone who read the description carelessly even filed a bug
report on it, do note that this matches substrings of each element of
`x`

(just as `grep`

does) and **not** whole
elements. See also `adist`

in package utils, which
optionally returns the offsets of the matched substrings.

##### See Also

`grep`

, `adist`

.
A different interface to approximate string matching is provided by
`aregexec()`

.

##### Examples

`library(base)`

```
# NOT RUN {
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)
# }
```

*Documentation reproduced from package base, version 3.6.1, License: Part of R 3.6.1*