hamming) counts the number of
character substitutions that turns b into a. If a
and b have different number of characters or if maxDist is
exceeded, Inf is returned.The Levenshtein distance (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. If maxDist is exceeded Inf is returned.
The Optimal String Alignment distance (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). If maxDist is exceeded Inf is returned.
The full Damerau-Levensthein distance (dl) allows for multiple
edits on substrings. If maxDist is exceeded Inf is returned.
The longest common substring 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. If maxDist is exceeded Inf is returned.
A $q$-gram 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 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 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
For the soundex method, 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.
a and b.