Example usage for com.mongodb.client.model Accumulators avg

Introduction

In this page you can find the example usage for com.mongodb.client.model Accumulators avg.

Prototype

public static <TExpression> BsonField avg(final String fieldName, final TExpression expression) 

Source Link

Document

Gets a field name for a $group operation representing the average of the values of the given expression when applied to all members of the group.

Usage

From source file:co.aurasphere.mongodb.university.classes.m101j.homework23.MainClass.java

License:Open Source License

/**
 * The main method./*from w w w .  j ava2  s  . c  o m*/
 *
 * @param args
 *            the arguments
 */
public static void main(String[] args) {

    MongoClient client = new MongoClient();
    MongoDatabase numbersDB = client.getDatabase("students");
    MongoCollection<Document> grades = numbersDB.getCollection("grades");

    // Gets all the grades.
    MongoCursor<Document> cursor = grades.find(Filters.eq("type", "homework"))
            .sort(Sorts.ascending("student_id", "score")).iterator();

    Object previousStudentId = null;
    try {
        // Finds the lowest homework score.
        while (cursor.hasNext()) {
            Document entry = cursor.next();

            // If the student_id is different from the previous one, this 
            // means that this is the student's lowest graded homework 
            // (they are sorted by score for each student).
            if (!entry.get("student_id").equals(previousStudentId)) {
                Object id = entry.get("_id");
                grades.deleteOne(Filters.eq("_id", id));

            }

            // The current document ID becomes the new previous one.   
            previousStudentId = entry.get("student_id");
        }

        // Gets the student with the highest average in the class.
        AggregateIterable<Document> results = grades
                .aggregate(Arrays.asList(Aggregates.group("$student_id", Accumulators.avg("average", "$score")),
                        Aggregates.sort(Sorts.descending("average")), Aggregates.limit(1)));

        // There should be only one result. Prints it.
        System.out.println("Solution : " + results.iterator().next().toJson());

    } finally {
        cursor.close();
    }

    client.close();
}

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From source file:co.aurasphere.mongodb.university.classes.m101j.homework31.MainClass.java

License:Open Source License

/**
 * The main method./*from  w  ww . j a  va  2s.  com*/
 *
 * @param args
 *            the arguments
 */
@SuppressWarnings("unchecked")
public static void main(String[] args) {
    MongoClient client = new MongoClient();
    MongoDatabase db = client.getDatabase("school");
    MongoCollection<Document> students = db.getCollection("students");

    // Gets all the students.
    MongoCursor<Document> cursor = students.find().iterator();

    try {
        while (cursor.hasNext()) {
            Document student = cursor.next();
            List<Document> scores = (List<Document>) student.get("scores");

            // Finds the lowest homework score.
            Document minScoreObj = null;
            double minScore = Double.MAX_VALUE;

            for (Document scoreDocument : scores) {
                double score = scoreDocument.getDouble("score");
                String type = scoreDocument.getString("type");

                // Swaps the scores.
                if (type.equals("homework") && score < minScore) {
                    minScore = score;
                    minScoreObj = scoreDocument;
                }
            }

            // Removes the lowest score.
            if (minScoreObj != null) {
                scores.remove(minScoreObj);
            }

            // Updates the record.
            students.updateOne(Filters.eq("_id", student.get("_id")),
                    new Document("$set", new Document("scores", scores)));
        }

        // Gets the student with the highest average in the class.
        AggregateIterable<Document> results = students.aggregate(Arrays.asList(Aggregates.unwind("$scores"),
                Aggregates.group("$_id", Accumulators.avg("average", "$scores.score")),
                Aggregates.sort(Sorts.descending("average")), Aggregates.limit(1)));

        // There should be only one result. Prints it.
        System.out.println("Solution : " + results.iterator().next().toJson());

    } finally {
        cursor.close();
    }

    client.close();
}

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