What is Inverted Indexing?
We can see it as a data structure that is used by most search engines to quickly find content or web pages which contain specific words or phrases. Here, a word in a document is indexed, along with a reference to the location of the word in the document. This is what makes it a faster search as it does not need to scan through each document entirely.

Hadoop Version used: Hadoop-3.2.1 Java Version used: 1.8.0_362

Steps to follow:

1. Made two sample files in a folder named as input in Downloads:
   sample1.txt
   5722018411 Hello World Bye World

   sample2.txt
   6722018415 Hello Hadoop Goodbye Hadoop

2. Make an input directory “input” command: hdfs dfs -mkdir /input

3. Put the sample files from Downloads/input to input directory in hadoop hdfs dfs –put /home/keshavgarg/Downloads/input/sample1.txt /input/ hdfs dfs –put /home/keshavgarg/Downloads/input/sample2.txt /input/

   Come to hadoop-3.2.1 folder using command 'Cd ..'

4. Then type the command: bin/hadoop jar share/hadoop/mapreduce/invertedindex.jar InvertedIndex /input /output

5. Type hdfs dfs -cat /input/part-r-00000

How to convert java file to jar file:

1. Add these line to the hadoop-env.sh or set them in terminal export PATH=${JAVA_HOME}/bin:${PATH} export HADOOP_CLASSPATH=${JAVA_HOME}/lib/tools.jar

2. Copy the InvertedIndex.java to Hadoop Distributed root folder

3. Then run these commands: bin/hadoop com.sun.tools.javac.Main InvertedIndex.java jar cf invertedindex.jar InvertedIndex*.class

4. It will create a jar file along with three class files, copy all of them in hadoop-3.2.1/share/hadoop/mapreduce