Home › Text › Phonetic encoding

The Metaphone code of one word.

public static string Encode(ReadOnlySpan<char> value)
public static string Encode(string value)

Parameters — value is a single word, or several separated by spaces. Case does not matter: the word is uppercased by the full case mapping and decomposed (NFKD), so é reads as E and ß as SS. A character no rule names — an apostrophe, a digit — writes nothing, but it still stands where it is, so it parts a doubled letter: Keats's keeps both of its S sounds. The string overload forwards to the span one.

Returns — string, a variable-length code drawn from B X S K J T F H L M N P R 0 W Y, with a space between the codes of two words, or the empty string when nothing in value sounds.

Exceptions — ArgumentNullException when value is null (the string overload only; a ReadOnlySpan<char> cannot be null). An empty string is accepted and encodes to the empty string.

Example — the digraphs that make the alphabet look strange.

using Lodestar.Text.Phonetics;

string th = Metaphone.Encode("Thomas");  // => 0MS
string sh = Metaphone.Encode("Christina");  // => XRSTN
string silent = Metaphone.Encode("Knight");  // => NT

Remarks — 0 and X are not placeholders. 0 is the "th" sound and X the "sh" sound, both written as single characters so a code stays one character per sound. This is why a Metaphone code must never be shown to a user: 0MS is correct and unreadable.

Knight → NT is the behaviour that distinguishes this from the other two encoders, and it is also the reason to prefer it for ordinary English words over Soundex.Encode. Silent k, w, g and b are all handled, along with GH, DGE, -TION and the rest of the spellings English uses for sounds it does not write plainly.

T goes silent before CH, and GH before a consonant: Fletcher is FLXR and Highness is HNS. Every rule is jellyfish's, on any input at all — a random letter sequence such as xhdzhumzj encodes to jellyfish's own XHTSHMSJ — which is what decision 0009 settles.

Applies to — net10.0, netstandard2.0.

See also — Metaphone, Soundex.Encode, the phonetics index.