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RussianSnowballStemmer

Russian stemming by the Snowball algorithm.

public static class RussianSnowballStemmer

Example — a noun and two of its twelve case forms, collapsed onto one key.

using Lodestar.Text.Stemming;

string nominative = RussianSnowballStemmer.Stem("город");  // => город
string genitive = RussianSnowballStemmer.Stem("города");  // => город
string instrumental = RussianSnowballStemmer.Stem("городами");  // => город

Remarks — Russian is the only Cyrillic stemmer here, and the one whose regions are measured differently from every other. Four things about it are worth knowing before reading a stem.

RV is the rest of the word after its first vowel, and nothing like the Romance RV, which counts letters two and three. Steps 1 and 2 search inside it, which is what stops a short word from being cut to nothing. R2 is measured the ordinary way and is used by step 3 alone; R1 is never used.

Step 1 is four tables tried in order. A perfective gerund ending ends the step on its own; otherwise a reflexive ся/сь comes off first, and then the first of an adjectival, a verb and a noun ending that matches. Three of those tables come in two groups, where the first group counts only when the letter before it is а or я — читаемый loses its ем and любимый does not.

ё is folded to е before the rules run. It is not a letter of the alphabet the algorithm is written on, so ёлка and елка are one key. Every other letter comes back as it went in, and every one of them is a single UTF-16 unit, so there is no code-point mode to choose.

One ending does not agree with the published description, deliberately. рискующая stems to рискующ and not to риск, because nltk's table misspells that one pair of 234 and parity with nltk is the contract — see decision 0006, which also names the one place this stemmer does not follow nltk.

Reference behaviour is nltk.stem.snowball.SnowballStemmer("russian"), matched over 291 words.

Applies to — net10.0, netstandard2.0.

See also — the stemming index.

Members

Member	What it does
RussianSnowballStemmer.Stem	The Snowball stem of one Russian word.