stringdist 0.8: now with soundex

August 22, 2014
By

(This article was first published on Mark van der Loo, and kindly contributed to R-bloggers)

An update to the stringdist package was released earlier this month. Thanks to a contribution of Jan van der Laan the package now includes a method to compute soundex codes as defined here. Briefly, soundex encoding aims to translate words that sound similar (when pronounced in English) to the same code.

Soundex codes can be computed with the new phonetic function, for example:

library(stringdist)
> phonetic(c('Euler','Gauss','Hilbert','Knuth','Lloyd','Lukasiewicz','Wachs'))
[1] "E460" "G200" "H416" "K530" "L300" "L222" "W200"

Two strings are considered equal when they have the same soundex code, we have a two-valued distance function.

> stringdist('Claire','Clare',method='soundex')
[1] 0
stringdist('Harry','Joe',method='soundex')
[1] 1

Since soundex is really only defined on the printable ASCII character set, a warning is given when non-ascii or non-printable ascii characters are encountered.

> phonetic("Jörgen")
[1] "J?62"
Warning message:
In phonetic("Jörgen") :
  soundex encountered 1 non-printable ASCII or non-ASCII
  characters. Results may be unreliable, see ?printable_ascii

The also new function printable_ascii can help you to detect such characters.

> printable_ascii(c("jörgen","jurgen"))
[1] FALSE  TRUE

To get rid of such characters in a sensible way there are a few options. First of all, you may want to try R's built-in iconv interface to translate accented characters to ascii.

> iconv("jörgen",to="ASCII//TRANSLIT")
[1] "jorgen"

However, behaviour of iconv may be system-dependent, see the iconv documentation for a thorough discussion. Another option is to install the stringi package.

library(stringi)
> stri_trans_general("jörgen","Latin-ASCII")
[1] "jorgen"

This package should yield the same result, regardless of the OS you're working on.

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