/**
* For each item, calculate the sequence id of sequences containing that item
*
* @param database the current sequence database
* @return Map of items to sequence IDs that contains each item
*/
private Map<Integer, Set<Integer>> findSequencesContainingItems(SequenceDatabase database) {
// We use a map to store the sequence IDs where an item appear
// Key : item Value : a set of sequence IDs
Map<Integer, Set<Integer>> mapSequenceID =
new HashMap<
Integer,
Set<
Integer>>(); // pour conserver les ID des séquences: <Id Item, Set d'id de
// séquences>
// for each sequence
for (Sequence sequence : database.getSequences()) {
// for each itemset in that sequence
for (List<Integer> itemset : sequence.getItemsets()) {
// for each item
for (Integer item : itemset) {
// get the set of sequence ids for that item
Set<Integer> sequenceIDs = mapSequenceID.get(item);
if (sequenceIDs == null) {
// if null create a new set
sequenceIDs = new HashSet<Integer>();
mapSequenceID.put(item, sequenceIDs);
}
// add the current sequence id to this set
sequenceIDs.add(sequence.getId());
}
}
}
return mapSequenceID;
}
/**
* This method generates statistics for a sequence database (a file)
*
* @param path the path to the file
* @throws IOException exception if there is a problem while reading the file.
*/
public void getStats(String path) throws IOException {
/////////////////////////////////////
// (1) First we will read the sequence database into memory.
// (actually, we don't really need to read it into memory because it
// just require a single pass, but the code is more simple like that
// - it could be optimized, if necessary).
///////////////////////////////////
List<Sequence> sequences =
new ArrayList<Sequence>(); // A sequence database is stored as a list of sequences
int maxItem = 0; // the largest id for items in the database
String thisLine; // a temporary variable to read each line from the file
BufferedReader myInput = null;
try {
// we read the file line by line
FileInputStream fin = new FileInputStream(new File(path));
myInput = new BufferedReader(new InputStreamReader(fin));
int i = 0; // used to count the lines.
// for each line until the end of the file
while ((thisLine = myInput.readLine()) != null) {
// we split the line according to spaces into tokens
String tokens[] = thisLine.split(" ");
// we create a new sequence object to store the sequence that correspond to this line.
Sequence sequence = new Sequence(i++);
// we create a list of integer to store the current itemset from the sequence
// that correspond to this line.
List<Integer> itemset = new ArrayList<Integer>();
// For each token
for (String token : tokens) {
// if the token starts with "<" it means that it is a timestamp
if (token.codePointAt(0) == '<') {
// we just ignore it for statistics..
}
// if the token is "-1" it means that it is the end of an itemset
else if (token.equals("-1")) {
// we add the itemset to the sequence
sequence.addItemset(itemset);
// we reset the variable itemset to read the next itemset
itemset = new ArrayList<Integer>();
}
// if the token is "-2", it indicates the end of this sequence and the
// end of the line
else if (token.equals("-2")) {
// we add the sequence to the list of sequences
sequences.add(sequence);
}
// otherwise, it means that the token is an item
else {
// we convert to an integer
Integer item = Integer.parseInt(token);
// we check if it has the largest value because we
// want to keep this information
if (item >= maxItem) {
maxItem = item;
}
// we add the item to the current itemset.
itemset.add(item);
}
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (myInput != null) {
myInput.close();
}
}
/////////////////////////////////////
// We finished reading the database into memory.
// We will calculate statistics on this sequence database.
///////////////////////////////////
System.out.println("============ SEQUENCE DATABASE STATS ==========");
System.out.println("Number of sequences : " + sequences.size());
// we initialize some variables that we will use to generate the statistics
java.util.Set<Integer> items = new java.util.HashSet<Integer>(); // the set of all items
List<Integer> sizes = new ArrayList<Integer>(); // the lengths of each sequence
List<Integer> itemsetsizes = new ArrayList<Integer>(); // the lengths of each itemset
List<Integer> differentitems =
new ArrayList<Integer>(); // the number of different item for each sequence
List<Integer> appearXtimesbySequence =
new ArrayList<
Integer>(); // the average number of times that items appearing in a sequence, appears
// in this sequence.
// Loop on sequences from the database
for (Sequence sequence : sequences) {
// we add the size of this sequence to the list of sizes
sizes.add(sequence.size());
// this map is used to calculate the number of times that each item
// appear in this sequence.
// the key is an item
// the value is the number of occurences of the item until now for this sequence
HashMap<Integer, Integer> mapIntegers = new HashMap<Integer, Integer>();
// Loop on itemsets from this sequence
for (List<Integer> itemset : sequence.getItemsets()) {
// we add the size of this itemset to the list of itemset sizes
itemsetsizes.add(itemset.size());
// Loop on items from this itemset
for (Integer item : itemset) {
// If the item is not in the map already, we set count to 0
Integer count = mapIntegers.get(item);
if (count == null) {
count = 0;
}
// otherwise we set the count to count +1
count = count + 1;
mapIntegers.put(item, count);
// finally, we add the item to the set of items
items.add(item);
}
}
// we add all items found in this sequence to the global list
// of different items for the database
differentitems.add(mapIntegers.entrySet().size());
// for each item appearing in this sequence,
// we put the number of times in a global list "appearXtimesbySequence"
// previously described.
for (Entry<Integer, Integer> entry : mapIntegers.entrySet()) {
appearXtimesbySequence.add(entry.getValue());
}
}
// we print the statistics
System.out.println("File " + path);
System.out.println("Number of distinct items: " + items.size());
System.out.println("Largest item id: " + maxItem);
System.out.println(
"Average number of itemsets per sequence : "
+ calculateMean(sizes)
+ " standard deviation: "
+ calculateStdDeviation(sizes)
+ " variance: "
+ calculateVariance(sizes));
System.out.println(
"Average number of distinct item per sequence : "
+ calculateMean(differentitems)
+ " standard deviation: "
+ calculateStdDeviation(differentitems)
+ " variance: "
+ calculateVariance(differentitems));
System.out.println(
"Average number of occurences in a sequence for each item appearing in a sequence : "
+ calculateMean(appearXtimesbySequence)
+ " standard deviation: "
+ calculateStdDeviation(appearXtimesbySequence)
+ " variance: "
+ calculateVariance(appearXtimesbySequence));
System.out.println(
"Average number of items per itemset : "
+ calculateMean(itemsetsizes)
+ " standard deviation: "
+ calculateStdDeviation(itemsetsizes)
+ " variance: "
+ calculateVariance(itemsetsizes));
}