| Method name |
| Description |
osa |
| Optimal string aligment, (restricted Damerau-Levenshtein distance). |
lv |
Levenshtein distance (as in R's native adist). |
dl |
| Full Damerau-Levenshtein distance. |
hamming |
Hamming distance (a and b must have same nr of characters). |
lcs |
| Longest common substring distance. |
qgram |
| $q$-gram distance. |
cosine |
| cosine distance between $q$-gram profiles |
jaccard |
| Jaccard distance between $q$-gram profiles |
jw |
| Jaro, or Jaro-Winker distance. |
method='hamming') counts the number of
character substitutions that turns b into a. If a
and b have different number of characters the distance is Inf. The Levenshtein distance (method='lv') counts the number of
deletions, insertions and substitutions necessary to turn b into
a. This method is equivalent to R's native adist
function. The Optimal String Alignment distance (method='osa') is like the Levenshtein
distance but also allows transposition of adjacent characters. Here, each
substring may be edited only once. (For example, a character cannot be transposed twice
to move it forward in the string). The full Damerau-Levensthein distance (method='dl') is like the optimal
string alignment distance except that it allows for multiple edits on substrings. The longest common substring (method='lcs') is defined as the longest string that can be
obtained by pairing characters from a and b while keeping the order
of characters intact. The lcs-distance is defined as the number of unpaired characters.
The distance is equivalent to the edit distance allowing only deletions and insertions,
each with weight one. A $q$-gram (method='qgram') is a subsequence of $q$ consecutive
characters of a string. If $x$ ($y$) is the vector of counts
of $q$-gram occurrences in a (b), the $q$-gram distance
is given by the sum over the absolute differences $|x_i-y_i|$.
The computation is aborted when q is is larger than the length of
any of the strings. In that case Inf is returned. The cosine distance (method='cosine') is computed as $1-x\cdot y/(\|x\|\|y\|)$, where $x$ and
$y$ were defined above. Let $X$ be the set of unique $q$-grams in a and $Y$ the set of unique
$q$-grams in b. The Jaccard distance (method='jaccard') is given by $1-|X\cap Y|/|X\cup Y|$. The Jaro distance (method='jw', p=0), is a number
between 0 (exact match) and 1 (completely dissimilar) measuring
dissimilarity between strings. It is defined to be 0 when both strings have
length 0, and 1 when there are no character matches between a and
b. Otherwise, the Jaro distance is defined as
$1-(1/3)(w_1m/|a| + w_2m/|b| + w_3(m-t)/m)$.
Here,$|a|$ indicates the number of characters in a, $m$ is
the number of character matches and $t$ the number of transpositions of
matching characters. The $w_i$ are weights associated with the characters
in a, characters in b and with transpositions. A character
$c$ of a matches a character from b when $c$
occurs in b, and the index of $c$ in a differs less than
$\max(|a|,|b|)/2 -1$ (where we use integer division) from the index of
$c$ in b. Two matching characters are transposed when they are
matched but they occur in different order in string a and b. The Jaro-Winkler distance (method=jw, 0) adds a
correction term to the Jaro-distance. It is defined as $d - l\cdot p\cdot d$, where
$d$ is the Jaro-distance. Here, $l$ is obtained by counting, from
the start of the input strings, after how many characters the first
character mismatch between the two strings occurs, with a maximum of four. The
factor $p$ is a penalty factor, which in the work of Winkler is often
chosen $0.1$. For the soundex distance (method='soundex'), strings are translated to a soundex code
(see phonetic for a specification). The
distance between strings is 0 when they have the same soundex code,
otherwise 1. Note that soundex recoding is only meaningful for characters
in the ranges a-z and A-Z. A warning is emitted when non-printable or non-ascii
characters are encountered. Also see printable_ascii. stringdist,
stringdistmatrix, amatch
seq_dist, seq_distmatrix, seq_amatch
stringdist-encoding