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+# Big Data Process Assignment 2 _ Meiqi GUO
+## Pre-processing the input
+
+For the part of pre-procesing, the input consists of：
+* the document corpus of [pg100.txt](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment2/blob/master/input/pg100.txt)
+* the [Stopword file](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment2/blob/master/input/Stopwords) which I made in the assignment 1
+* the [Words with frequency file](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment2/blob/master/input/wordfreq) of pg100.txt that I obtained by runnning the assignment 1 with a slight changement of [MyWordCount.java](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment1/blob/master/MyWordCount.java).
+
+
+I do the following tasks in [Preprocess.java](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment2/blob/master/output/Preprocess.java):
+
+
+**STEP 1: Remove all stopwords**
+```
+else if (stopWords.contains(word)){
+        		 continue;
+        		 }
+```
+
+**STEP 2: Remove special characters (keep only [a-z],[A-Z] and [0-9]) and convert to lower case**
+```
+word.set(token.replaceAll("[^A-Za-z0-9]+", "").toLowerCase())
+```
+
+**STEP 3：Keep each unique word only once per line**
+
+
+We define a *hashset* where we store words
+```
+Set<String> wordSet = new HashSet<String>();
+```
+
+**STEP 4: Remove empty lines**
+
+
+I removed firstly all empty lines:
+```
+if (value.toString().isEmpty()){
+    		 return;
+    	 }	
+```
+
+After removing stopwords and special characters, I removed all new empty lines:
+```
+if (wordSet.isEmpty()){
+        	 return;
+```
+**STEP 5: Count line numbers**
+
+
+I used two counters:
+* one is to note the number of lines in the initial document, named *LineNumCounter*; 
+* the other one is to record the number of lines for the output, named *FinalLineNumCounter*, which means the number after removing all empty lines. 
+
+The result is shown as below:
+
+NUM = 124787
+
+Final_NUM = 114815
+
+So nearly 10000 lines are empty.
+
+
+![](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment2/blob/master/output/counters.PNG)
+
+
+**STEP 6: Order the tokens of each line in ascending order of global frequency**
+
+I used the [Words with frequency file](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment2/blob/master/input/wordfreq) of pg100.txt that I obtained by runnning the assignment 1 with a slight changement of [MyWordCount](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment1/blob/master/MyWordCount.java) as input and ordered tokens by their frequency.
+```
+Collections.sort(wordList, new Comparator<String>() {
+        	 @Override
+        	 public int compare(String s1, String s2)
+        	 {
+        		 return  wordFreq.get(s1).compareTo(wordFreq.get(s2));
+        	 }
+         });
+```
+
+You can see the output file [here](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment2/blob/master/output/output_preprocess).
+
+
+All the details are written in my code [Preprocess.java](https://gitlab.my.ecp.fr/2014guom/BigDataProcessAssignment2/blob/master/output/Preprocess.java).
+