src/Lucene.Net.Analysis.Common/Analysis/Id/IndonesianStemmer.cs

// Lucene version compatibility level 4.8.1
using Lucene.Net.Analysis.Util;

namespace Lucene.Net.Analysis.Id
{
    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You under the Apache License, Version 2.0
     * (the "License"); you may not use this file except in compliance with
     * the License.  You may obtain a copy of the License at
     *
     *     http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    /// <summary>
    /// Stemmer for Indonesian.
    /// <para>
    /// Stems Indonesian words with the algorithm presented in:
    /// <c>A Study of Stemming Effects on Information Retrieval in
    /// Bahasa Indonesia</c>, Fadillah Z Tala.
    /// http://www.illc.uva.nl/Publications/ResearchReports/MoL-2003-02.text.pdf
    /// </para>
    /// </summary>
    public class IndonesianStemmer
    {
        private int numSyllables;
        private int flags;
        private const int REMOVED_KE = 1;
        private const int REMOVED_PENG = 2;
        private const int REMOVED_DI = 4;
        private const int REMOVED_MENG = 8;
        private const int REMOVED_TER = 16;
        private const int REMOVED_BER = 32;
        private const int REMOVED_PE = 64;

        /// <summary>
        /// Stem a term (returning its new length).
        /// <para>
        /// Use <paramref name="stemDerivational"/> to control whether full stemming
        /// or only light inflectional stemming is done.
        /// </para>
        /// </summary>
        public virtual int Stem(char[] text, int length, bool stemDerivational)
        {
            flags = 0;
            numSyllables = 0;
            for (int i = 0; i < length; i++)
            {
                if (IsVowel(text[i]))
                {
                    numSyllables++;
                }
            }

            if (numSyllables > 2)
            {
                length = RemoveParticle(text, length);
            }
            if (numSyllables > 2)
            {
                length = RemovePossessivePronoun(text, length);
            }

            if (stemDerivational)
            {
                length = StemDerivational(text, length);
            }
            return length;
        }

        private int StemDerivational(char[] text, int length)
        {
            int oldLength = length;
            if (numSyllables > 2)
            {
                length = RemoveFirstOrderPrefix(text, length);
            }
            if (oldLength != length) // a rule is fired
            {
                oldLength = length;
                if (numSyllables > 2)
                {
                    length = RemoveSuffix(text, length);
                }
                if (oldLength != length) // a rule is fired
                {
                    if (numSyllables > 2)
                    {
                        length = RemoveSecondOrderPrefix(text, length);
                    }
                }
            } // fail
            else
            {
                if (numSyllables > 2)
                {
                    length = RemoveSecondOrderPrefix(text, length);
                }
                if (numSyllables > 2)
                {
                    length = RemoveSuffix(text, length);
                }
            }
            return length;
        }

        private static bool IsVowel(char ch) // LUCENENET: CA1822: Mark members as static
        {
            switch (ch)
            {
                case 'a':
                case 'e':
                case 'i':
                case 'o':
                case 'u':
                    return true;
                default:
                    return false;
            }
        }

        private int RemoveParticle(char[] text, int length)
        {
            if (StemmerUtil.EndsWith(text, length, "kah") ||
                StemmerUtil.EndsWith(text, length, "lah") ||
                StemmerUtil.EndsWith(text, length, "pun"))
            {
                numSyllables--;
                return length - 3;
            }

            return length;
        }

        private int RemovePossessivePronoun(char[] text, int length)
        {
            if (StemmerUtil.EndsWith(text, length, "ku") || StemmerUtil.EndsWith(text, length, "mu"))
            {
                numSyllables--;
                return length - 2;
            }

            if (StemmerUtil.EndsWith(text, length, "nya"))
            {
                numSyllables--;
                return length - 3;
            }

            return length;
        }

        private int RemoveFirstOrderPrefix(char[] text, int length)
        {
            if (StemmerUtil.StartsWith(text, length, "meng"))
            {
                flags |= REMOVED_MENG;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 4);
            }

            if (StemmerUtil.StartsWith(text, length, "meny") && length > 4 && IsVowel(text[4]))
            {
                flags |= REMOVED_MENG;
                text[3] = 's';
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "men"))
            {
                flags |= REMOVED_MENG;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "mem"))
            {
                flags |= REMOVED_MENG;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "me"))
            {
                flags |= REMOVED_MENG;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 2);
            }

            if (StemmerUtil.StartsWith(text, length, "peng"))
            {
                flags |= REMOVED_PENG;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 4);
            }

            if (StemmerUtil.StartsWith(text, length, "peny") && length > 4 && IsVowel(text[4]))
            {
                flags |= REMOVED_PENG;
                text[3] = 's';
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "peny"))
            {
                flags |= REMOVED_PENG;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 4);
            }

            if (StemmerUtil.StartsWith(text, length, "pen") && length > 3 && IsVowel(text[3]))
            {
                flags |= REMOVED_PENG;
                text[2] = 't';
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 2);
            }

            if (StemmerUtil.StartsWith(text, length, "pen"))
            {
                flags |= REMOVED_PENG;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "pem"))
            {
                flags |= REMOVED_PENG;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "di"))
            {
                flags |= REMOVED_DI;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 2);
            }

            if (StemmerUtil.StartsWith(text, length, "ter"))
            {
                flags |= REMOVED_TER;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "ke"))
            {
                flags |= REMOVED_KE;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 2);
            }

            return length;
        }

        private int RemoveSecondOrderPrefix(char[] text, int length)
        {
            if (StemmerUtil.StartsWith(text, length, "ber"))
            {
                flags |= REMOVED_BER;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (length == 7 && StemmerUtil.StartsWith(text, length, "belajar"))
            {
                flags |= REMOVED_BER;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "be") && length > 4
                && !IsVowel(text[2]) && text[3] == 'e' && text[4] == 'r')
            {
                flags |= REMOVED_BER;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 2);
            }

            if (StemmerUtil.StartsWith(text, length, "per"))
            {
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (length == 7 && StemmerUtil.StartsWith(text, length, "pelajar"))
            {
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 3);
            }

            if (StemmerUtil.StartsWith(text, length, "pe"))
            {
                flags |= REMOVED_PE;
                numSyllables--;
                return StemmerUtil.DeleteN(text, 0, length, 2);
            }

            return length;
        }

        private int RemoveSuffix(char[] text, int length)
        {
            if (StemmerUtil.EndsWith(text, length, "kan")
                && (flags & REMOVED_KE) == 0
                && (flags & REMOVED_PENG) == 0
                && (flags & REMOVED_PE) == 0)
            {
                numSyllables--;
                return length - 3;
            }

            if (StemmerUtil.EndsWith(text, length, "an")
                && (flags & REMOVED_DI) == 0
                && (flags & REMOVED_MENG) == 0
                && (flags & REMOVED_TER) == 0)
            {
                numSyllables--;
                return length - 2;
            }

            if (StemmerUtil.EndsWith(text, length, "i")
                && !StemmerUtil.EndsWith(text, length, "si")
                && (flags & REMOVED_BER) == 0
                && (flags & REMOVED_KE) == 0
                && (flags & REMOVED_PENG) == 0)
            {
                numSyllables--;
                return length - 1;
            }
            return length;
        }
    }
}