Soundex implementations in .Net
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SoundEx algorithms

A .Net implementation of various SoundEx algorithms.

Copyright (c) Richard Birkby, 2002-2012. Apache licensed.


Every computer scientist has heard of SoundEx. It is perhaps the most infamous text processing/searching algorithm around. SoundEx promises a great deal - that of matching words with similar sounding words, but actually delivers, at best, a large number of inaccurate matches. Even though SoundEx was patented, variations have arisen, whether through poor understanding of the algorithm or through attempts to improve its accuracy. Thus, this article presents four popular implementations of SoundEx written in C# and .Net to allow you to perform your own benchmarking on your own data sets.


SoundEx was originally invented to find alternative spellings for surnames. The problem came from mis-spellings on US census returns and therefore the SoundEx algorithms are biased towards English speaking names. There are further variants for some western European languages, but in general the algorithm has never been considered a panacea for all fuzzy text matching.

Core algorithm

Most SoundEx algorithms are a variant on the following

  • Retain the first letter of the name
  • Drop all vowels, and h, y in all but the first letter
  • Replace b,f,p,v with the number 1
  • Replace c,g,j,k,q,s,x,z with the number 2
  • Replace d and t with the number 3
  • Replace l with 4, m and n with 5 and r with 6
  • Finally convert to a 4 character code like {letter}{number}{number}{number} by truncation

Some algorithms have grouping and adjacent letter rules in addition.