Task: Inverted index



C#: using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

class InvertedIndex
{
    static Dictionary<TItem, IEnumerable<TKey>> Invert<TKey, TItem>(Dictionary<TKey, IEnumerable<TItem>> dictionary)
    {
        return dictionary
            .SelectMany(keyValuePair => keyValuePair.Value.Select(item => new KeyValuePair<TItem, TKey>(item, keyValuePair.Key)))
            .GroupBy(keyValuePair => keyValuePair.Key)
            .ToDictionary(group => group.Key, group => group.Select(keyValuePair => keyValuePair.Value));
    }

    static void Main()
    {
        Console.Write("files: ");
        var files = Console.ReadLine();
        Console.Write("find: ");
        var find = Console.ReadLine();
        var dictionary = files.Split().ToDictionary(file => file, file => File.ReadAllText(file).Split().AsEnumerable());
        Console.WriteLine("{0} found in: {1}", find, string.Join(" ", Invert(dictionary)[find]));
    }
}



Java: package org.rosettacode;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class InvertedIndex {

    List<String> stopwords = Arrays.asList("a", "able", "about",
            "across", "after", "all", "almost", "also", "am", "among", "an",
            "and", "any", "are", "as", "at", "be", "because", "been", "but",
            "by", "can", "cannot", "could", "dear", "did", "do", "does",
            "either", "else", "ever", "every", "for", "from", "get", "got",
            "had", "has", "have", "he", "her", "hers", "him", "his", "how",
            "however", "i", "if", "in", "into", "is", "it", "its", "just",
            "least", "let", "like", "likely", "may", "me", "might", "most",
            "must", "my", "neither", "no", "nor", "not", "of", "off", "often",
            "on", "only", "or", "other", "our", "own", "rather", "said", "say",
            "says", "she", "should", "since", "so", "some", "than", "that",
            "the", "their", "them", "then", "there", "these", "they", "this",
            "tis", "to", "too", "twas", "us", "wants", "was", "we", "were",
            "what", "when", "where", "which", "while", "who", "whom", "why",
            "will", "with", "would", "yet", "you", "your");

    Map<String, List<Tuple>> index = new HashMap<String, List<Tuple>>();
    List<String> files = new ArrayList<String>();

    public void indexFile(File file) throws IOException {
        int fileno = files.indexOf(file.getPath());
        if (fileno == -1) {
            files.add(file.getPath());
            fileno = files.size() - 1;
        }

        int pos = 0;
        BufferedReader reader = new BufferedReader(new FileReader(file));
        for (String line = reader.readLine(); line != null; line = reader
                .readLine()) {
            for (String _word : line.split("\\W+")) {
                String word = _word.toLowerCase();
                pos++;
                if (stopwords.contains(word))
                    continue;
                List<Tuple> idx = index.get(word);
                if (idx == null) {
                    idx = new LinkedList<Tuple>();
                    index.put(word, idx);
                }
                idx.add(new Tuple(fileno, pos));
            }
        }
        System.out.println("indexed " + file.getPath() + " " + pos + " words");
    }

    public void search(List<String> words) {
        for (String _word : words) {
            Set<String> answer = new HashSet<String>();
            String word = _word.toLowerCase();
            List<Tuple> idx = index.get(word);
            if (idx != null) {
                for (Tuple t : idx) {
                    answer.add(files.get(t.fileno));
                }
            }
            System.out.print(word);
            for (String f : answer) {
                System.out.print(" " + f);
            }
            System.out.println("");
        }
    }

    public static void main(String[] args) {
        try {
            InvertedIndex idx = new InvertedIndex();
            for (int i = 1; i < args.length; i++) {
                idx.indexFile(new File(args[i]));
            }
            idx.search(Arrays.asList(args[0].split(",")));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private class Tuple {
        private int fileno;
        private int position;

        public Tuple(int fileno, int position) {
            this.fileno = fileno;
            this.position = position;
        }
    }
}