Section navigation

Analysis overview

Use this section when turning application text into searchable terms. Start with analysers, then choose tokenisers and filters only when the default pipeline does not fit.

Analysis turns raw text into the terms LeanCorpus stores and queries. Use the same pipeline at index-time and query-time so terms line up.

The parts

Component Role Starting point
IAnalyser End-to-end pipeline StandardAnalyser, StemmedAnalyser, LanguageAnalyser, IcuAnalyser
ITokeniser Splits input into tokens Tokeniser, Uax29UrlEmailTokeniser, IcuTokeniser
ITokenFilter Rewrites or drops tokens LowercaseFilter, StopWordFilter, SynonymGraphFilter
ICharFilter Rewrites input text before tokenisation HtmlStripCharFilter, MappingCharFilter, PatternReplaceCharFilter
IStemmer Reduces tokens to root forms EnglishStemmer, FrenchStemmer, GermanStemmer

What to start with

  • StandardAnalyser for general text with lowercase and stop-word removal.
  • StemmedAnalyser for English text where broader recall matters.
  • AnalyserFactory.Create("en") (or another language code) for a built-in language pipeline.
  • IcuAnalyser or IcuTokeniser when Unicode segmentation matters.
  • Analyser directly for a custom tokeniser and filter chain.

English stemming choices

Type Behaviour When
EnglishStemmer Porter-based Default for English. Used by AnalyserFactory.Create("en").
LightEnglishStemmer Lighter suffix stripping When Porter is too aggressive.
KStemmer Lexicon-validated (Krovetz-inspired) When false stems cost more than missed stems. Needs KStemLexicon.FromFile.

StemmedAnalyser also uses Porter stemming.

Custom pipeline

using Rowles.LeanCorpus.Analysis;
using Rowles.LeanCorpus.Analysis.Filters;
using Rowles.LeanCorpus.Analysis.Tokenisers;

var analyser = new Analyser(
    tokeniser: new Uax29UrlEmailTokeniser(),
    new LowercaseFilter(),
    new StopWordFilter(StopWords.English),
    new SynonymGraphFilter(new SynonymMap(new Dictionary<string, string[]>
    {
        ["tv"] = ["television"]
    })));

See also

Edit this page