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Scala for Data Science

You're reading from   Scala for Data Science Leverage the power of Scala with different tools to build scalable, robust data science applications

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Product type Paperback
Published in Jan 2016
Publisher
ISBN-13 9781785281372
Length 416 pages
Edition 1st Edition
Languages
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Author (1):
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Pascal Bugnion Pascal Bugnion
Author Profile Icon Pascal Bugnion
Pascal Bugnion
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Toc

Table of Contents (17) Chapters Close

Preface 1. Scala and Data Science FREE CHAPTER 2. Manipulating Data with Breeze 3. Plotting with breeze-viz 4. Parallel Collections and Futures 5. Scala and SQL through JDBC 6. Slick – A Functional Interface for SQL 7. Web APIs 8. Scala and MongoDB 9. Concurrency with Akka 10. Distributed Batch Processing with Spark 11. Spark SQL and DataFrames 12. Distributed Machine Learning with MLlib 13. Web APIs with Play 14. Visualization with D3 and the Play Framework A. Pattern Matching and Extractors Index

Complex queries


We now know how to convert DBObject instances to custom Scala classes. In this section, you will learn how to construct queries that only return a subset of the documents in the collection.

In the previous section, you learned to retrieve all the documents in a collection as follows:

scala> val objs = collection.find().toList
List[DBObject] = List({ "_id" : { "$oid" : "56365cec46f9534fae8ffd7f"} ,...

The collection.find() method returns an iterator over all the documents in the collection. By calling .toList on this iterator, we materialize it to a list.

We can customize which documents are returned by passing a query document to the .find method. For instance, we can retrieve documents for a specific login name:

scala> val query = DBObject("login" -> "mojombo")
query: DBObject = { "login" : "mojombo"}

scala> val objs = collection.find(query).toList
List[DBObject] = List({ "_id" : { "$oid" : "562e922546f953739c43df02"} , "login" : "mojombo",...

MongoDB queries...

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