February 2017
Beginner to intermediate
1100 pages
25h 19m
English
book
Scala: Guide for Data Science Professionals
by Pascal Bugnion, Arun Manivannan, Patrick R. Nicolas
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Aggregations with "Group by"
Slick also provides a groupBy method that behaves like the
groupBy method of native Scala collections. Let's get a list of candidates with all the donations for each candidate:
scala> val grouped = Tables.transactions.groupBy { _.candidate } grouped: scala.slick.lifted.Query[(scala.slick.lifted.Column[... scala> val aggregated = grouped.map { case (candidate, group) => (candidate -> group.map { _.amount }.sum) } aggregated: scala.slick.lifted.Query[(scala.slick.lifted.Column[... scala> val groupedDonations = db.withSession { implicit session => aggregated.list } groupedDonations: List[(String, Option[Long])] = List((Bachmann, Michele,Some(7439272)),...
Let's break this down. The first statement, transactions.groupBy ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.