Approximate matching and string distance calculations for R.

Current CRAN version: 0.5.0

String distance functions are scattered around R, and R's packages. Moreover, approximate string matching functions are scarce. The package offers four main functions:

• stringdist computes pairwise distances between two input character vectors (shorter one is recycled)
• stringdistmatrix computes the distance matrix between two input character vectors, optionally running in parallel.
• amatch is a fuzzy matching equivalent of R's native match function
• ain is a fuzzy matching equivalent of R's native %in% operator

These functions are built upon C-code that re-implements some common (weighted) string distance functions. As of version >0.5, distance functions include:

• Hamming distance;
• Levenshtein distance (weighted);
• Restricted Damerau-Levenshtein distance (weighted, a.k.a. Optimal String Alignment);
• Full Damerau-Levenshtein distance (weighted);
• Longest Common Substring distance;
• Q-gram distance (two implementations using different q-gram storage solutions; currently one is exposed).
• cosine distance for q-gram count vectors (= 1-cosine similarity)
• Jaccard distance for q-gram count vectors (= 1-Jaccard similarity)
• Jaro, and Jaro-Winker distance

To my best knowledge, the latter six were not available before in R.

Besides the above the function qgrams tabulates the qgrams in a charcter vector.

Up to version <=0.5, stringdist returned -1 to indicate that either

• maxDist is exceeded, or
• the distance is undefined between two input strings

From version >=0.6, this will be replaced by Inf. The main reason:

• This allows easier comparison using < and <=

The old convention stemmed from the fact that some distances (e.g. q-gram, hamming) are strictly integers. I'm abandoning this expressing all distances as double (R numeric) which allows me to use Inf.

To install the latest release from CRAN, open an R terminal and type

install.packages('stringdist')

To obtain the package from source code open a bash terminal (or git bash if you work under Windows with msysgit) and type

$> git clone https://github.com/markvanderloo/stringdist.git
$> cd stringdist
$> bash ./build.bash
$> R CMD INSTALL output/stringdist_*.tar.gz

Warning: the github version can change any time and may not even build properly. As most of the code is written in C, the development version may crash your R-session.