double_metaphone implements a fast version of Lawrence Philips' Double Metaphone Search Algorithm, a type of "sound alike" algorithm. This algorithm converts a word into phonetic keys, which should be the same for words pronounced similarly. Double Metaphone is widely used in spell checkers, search engines and genealogy sites.

I've implemented this search in modern C++11, with a focus on usability, testability and speed. Running on a 2.26GHz Intel Core 2 Duo, the search reaches 2,000,000 words per second.

Use

Header includes:

#include "double_metaphone.h"

Phonetic keys for words:

auto keys = dm::double_metaphone("Angier");
assert(keys.first == "ANJ"); // main key
assert(keys.second == "ANJR"); // alternate key

Phonetic key parts and their corresponding ranges in the original word:

int index = 0;
dm::double_metaphone(
  "Angier",
  [&](const char* metaph1, const char* metaph2, int start, int len)
  {
    switch (index++)
    {
      case 0:
        assert(strcmp(metaph1, "A") == 0 && strcmp(metaph2, "A") == 0);
        assert(start == 0 && len == 1); // corresponds to "A" in "Angier"
        break;
      case 1:
        assert(strcmp(metaph1, "N") == 0 && strcmp(metaph2, "N") == 0);
        assert(start == 1 && len == 1); // corresponds to "n" in "Angier"
        break;
      case 2:
        assert(strcmp(metaph1, "J") == 0 && strcmp(metaph2, "J") == 0);
        assert(start == 2 && len == 1); // corresponds to "g" in "Angier"
        break;
      case 3:
        assert(metaph1 == nullptr && metaph2 == nullptr);
        assert(start == 3 && len == 1); // corresponds to "i" in "Angier"
        break;
      case 4:
        assert(metaph1 == nullptr && metaph2 == nullptr);
        assert(start == 4 && len == 1); // corresponds to "e" in "Angier"
        break;
      case 5:
        assert(metaph1 == nullptr && strcmp(metaph2, "R") == 0);
        assert(start == 5 && len == 1); // corresponds to "r" in "Angier"
        break;
    }
  });

Require

Any C++11 toolchain, e.g. clang 3.3, gcc 4.8.

Install

double_metaphone is header only, just copy double_metaphone.h into your own sources.

To keep up to date in your git-managed project:

# once only
git remote add double_metaphone [email protected]:pixelglow/double_metaphone.git
git subtree add --prefix=double_metaphone double_metaphone master
# whenever double_metaphone changes
git subtree pull --prefix=double_metaphone double_metaphone master

Test

On clang:

clang++ -std=c++11 -stdlib=libc++ test.cpp -otest && ./test

On gcc:

g++ -std=c++11 test.cpp -otest && ./test

Design

The main differences over similar implementations:

• Standard C++11 with modern idioms like namespaces, lambdas, std::string and std::pair.
• Support for UTF-8 input.
• Callback API for phonetic key parts and their corresponding ranges in the original word.
• Each key part is generally either all vowels or all consonants.
• Tuned for speed.

Copyright

Copyright (c) 2014, Pixelglow Software. All rights reserved.

Original is copyright (c) 1998, 1999, Lawrence Philips. Slightly modified by Kevin Atkinson to fix several bugs and to allow it to give back more than 4 characters.

Tests are based on data from Stephen Woodbridge's version.

License

double_metaphone is licensed with the BSD license.

Support

• Follow us on Twitter: @pixelglow.
• Raise an issue on double_metaphone issues.

Donate

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