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FinnishSnowballStemmer

Finnish stemming by the Snowball algorithm.

public static class FinnishSnowballStemmer

Example — a noun in four of its fifteen cases, collapsed onto one key.

using Lodestar.Text.Stemming;

string inessive = FinnishSnowballStemmer.Stem("talossa");  // => talo
string adessive = FinnishSnowballStemmer.Stem("talolla");  // => talo
string illative = FinnishSnowballStemmer.Stem("taloon");  // => talo
string possessive = FinnishSnowballStemmer.Stem("talonsa");  // => talo

Remarks — Finnish is the longest of the twelve, and the reason is grammatical rather than incidental: it is agglutinative, so one noun carries fifteen cases, and each of those can take a possessive and then a particle on top. The algorithm peels them in that order — six steps over standard R1 and R2, with no floor and no RV region.

The steps come off in the order they went on. Particles first (-kin, -ko, -han), then possessives (-ni, -nsa, -mme), then cases, then comparatives, then plurals, then a tidying pass. talossaan gives up its -an as a possessive and only then its -ssa as a case, which is why a word can lose three endings in one pass and still reach the same key as the bare stem.

Vowel harmony decides which list applies. Finnish suffixes come in back and front pairs, and the algorithm keeps them apart: -ssa after a back vowel, -ssä after a front one, and a possessive -an that follows only the first while -än follows only the second. This is what the other eleven languages have no equivalent of.

Three of the steps read what sits in front of the ending. hXn needs its own vowel repeated before it, -siin needs a vowel and an i, -seen needs a long vowel, and the partitive -a needs a consonant and a vowel. A condition that fails leaves the word alone rather than falling through to a shorter ending — with four measured exceptions, in decision 0090.

The last step is what makes a Finnish stem look short. It removes a long vowel, then a consonant and one of a ä e i, then an -oj, -uj or -jo, and finally the second letter of any doubled consonant — so kissaa reaches kis and kotimaahan reaches kotim.

Reference behaviour is nltk.stem.snowball.SnowballStemmer("finnish"), matched over 217 words.

Applies to — net10.0, netstandard2.0.

See also — the stemming index.

Members

Member	What it does
FinnishSnowballStemmer.Stem	The Snowball stem of one Finnish word.