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)
agrepl(pattern, x, max.distance = 0.1, costs = NULL,
ignore.case = FALSE, fixed = TRUE, useBytes = FALSE)
Arguments
pattern
a non-empty character string to be matched. For
fixed = FALSE this should contain an extended
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.
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. If TRUE the matching is done
byte-by-byte rather than character-by-character. See
‘Details’.
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 the tre code by Ville Laurikari
(https://github.com/laurikari/tre), which supports MBCS
character matching.
The main effect of useBytes = TRUE 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.
Author(s)
Original version in R < 2.10.0 by David Meyer. Current version by Brian Ripley and Kurt Hornik.
See Also
grep , adist .
A different interface to approximate string matching is provided by
aregexec().
Examples
agrep("lasy", "1 lazy 2")
agrep("lasy", c(" 1 lazy 2", "1 lasy 2"), max.distance = list(sub = 0))
agrep("laysy", c("1 lazy", "1", "1 LAZY"), max.distance = 2)
agrep("laysy", c("1 lazy", "1", "1 LAZY"), max.distance = 2, value = TRUE)
agrep("laysy", c("1 lazy", "1", "1 LAZY"), max.distance = 2, ignore.case = TRUE)