1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
|
% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/afind.R
\name{afind}
\alias{afind}
\alias{grab}
\alias{grabl}
\alias{extract}
\title{Stringdist-based fuzzy text search}
\usage{
afind(
x,
pattern,
window = NULL,
value = TRUE,
method = c("osa", "lv", "dl", "hamming", "lcs", "qgram", "cosine", "running_cosine",
"jaccard", "jw", "soundex"),
useBytes = FALSE,
weight = c(d = 1, i = 1, s = 1, t = 1),
q = 1,
p = 0,
bt = 0,
nthread = getOption("sd_num_thread")
)
grab(x, pattern, maxDist = Inf, value = FALSE, ...)
grabl(x, pattern, maxDist = Inf, ...)
extract(x, pattern, maxDist = Inf, ...)
}
\arguments{
\item{x}{strings to search in}
\item{pattern}{strings to find (not a regular expression). For \code{grab},
\code{grabl}, and \code{extract} this must be a single string.}
\item{window}{width of moving window.}
\item{value}{toggle return matrix with matched strings.}
\item{method}{Matching algorithm to use. See \code{\link{stringdist-metrics}}.}
\item{useBytes}{Perform byte-wise comparison. See \code{\link{stringdist-encoding}}.}
\item{weight}{For \code{method='osa'} or \code{'dl'}, the penalty for
deletion, insertion, substitution and transposition, in that order. When
\code{method='lv'}, the penalty for transposition is ignored. When
\code{method='jw'}, the weights associated with characters of \code{a},
characters from \code{b} and the transposition weight, in that order.
Weights must be positive and not exceed 1. \code{weight} is ignored
completely when \code{method='hamming'}, \code{'qgram'}, \code{'cosine'},
\code{'Jaccard'}, \code{'lcs'}, or \code{'soundex'}.}
\item{q}{q-gram size, only when method is \code{'qgram'}, \code{'jaccard'},
or \code{'cosine'}.}
\item{p}{Winklers 'prefix' parameter for Jaro-Winkler distance, with
\eqn{0\leq p\leq0.25}. Only when method is \code{'jw'}}
\item{bt}{Winkler's boost threshold. Winkler's prefix factor is
only applied when the Jaro distance is larger than \code{bt}.
Applies only to \code{method='jw'} and \code{p>0}.}
\item{nthread}{Number of threads used by the underlying C-code. A sensible
default is chosen, see \code{\link{stringdist-parallelization}}.}
\item{maxDist}{Only windows with distance \code{<= maxDist} are considered a match.}
\item{...}{passed to \code{afind}.}
}
\value{
For \code{afind}: a \code{list} of three matrices, each with
\code{length(x)} rows and \code{length(pattern)} columns. In each matrix,
element \eqn{(i,j)} corresponds to \code{x[i]} and \code{pattern[j]}. The
names and description of each matrix is as follows.
\itemize{
\item{\code{location}. \code{[integer]}, location of the start of best matching window.
When \code{useBytes=FALSE}, this corresponds to the location of a \code{UTF} code point
in \code{x}, possibly after conversion from its original encoding.}
\item{\code{distance}. \code{[character]}, the string distance between pattern and
the best matching window.}
\item{\code{match}. \code{[character]}, the first, best matching window.}
}
For \code{grab}, an \code{integer} vector, indicating in which elements of
\code{x} a match was found with a distance \code{<= maxDist}. The matched
values when \code{value=TRUE} (equivalent to \code{\link[base]{grep}}).
For \code{grabl}, a \code{logical} vector, indicating in which elements of
\code{x} a match was found with a distance \code{<= maxDist}. (equivalent
to \code{\link[base:grep]{grepl}}).
For \code{extract}, a \code{character} matrix with \code{length(x)} rows and
\code{length(pattern)} columns. If match was found, element \eqn{(i,j)}
contains the match, otherwise it is set to \code{NA}.
}
\description{
\code{afind} slides a window of fixed width over a string \code{x} and
computes the distance between the each window and the sought-after
\code{pattern}. The location, content, and distance corresponding to the
window with the best match is returned.
}
\details{
Matching is case-sensitive. Both \code{x} and \code{pattern} are converted
to \code{UTF-8} prior to search, unless \code{useBytes=TRUE}, in which case
the distances are measured bytewise.
Code is parallelized over the \code{x} variable: each value of \code{x}
is scanned for every element in \code{pattern} using a separate thread (when \code{nthread}
is larger than 1).
The functions \code{grab} and \code{grabl} are approximate string matching
functions that somewhat resemble base R's \code{\link[base]{grep}} and
\code{\link[base:grep]{grepl}}. They are implemented as convenience wrappers
of \code{afind}.
}
\section{Running cosine distance}{
This algorithm gains efficiency by using that two consecutive windows have
a large overlap in their q-gram profiles. It gives the same result as
the \code{"cosine"} distance, but much faster.
}
\examples{
texts = c("When I grow up, I want to be"
, "one of the harvesters of the sea"
, "I think before my days are gone"
, "I want to be a fisherman")
patterns = c("fish", "gone","to be")
afind(texts, patterns, method="running_cosine", q=3)
grabl(texts,"grew", maxDist=1)
extract(texts, "harvested", maxDist=3)
}
\seealso{
Other matching:
\code{\link{amatch}()}
}
\concept{matching}
|
