August 2015
Intermediate to advanced
312 pages
7h 28m
Japanese
Content preview from 初めてのSpark
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60
4 章 キー／値ペアの処理
4.4
ア
RDD
るアクン
変換と同様に、ベースの
RDD
で使える通常のアクションは、ペア
RDD
でも使うことができま
す。ペア
RDD
で使えるアクションはそれ以外にもあり、データがキー／値形式になっていること
の利点を生かすことができます。
4-3
を参照してください。
4-3
RDD
({(1, 2), (3, 4), (3, 6)})
countByKey()
キーごとの要素数をカウントする。
rdd.countByKey() {(1, 1),
(3, 2)
}
collectAsMap()
容易にルックアップできるよう、結果を
map
として返す。同じキーのエントリが複数ある
場合は、そのうち
1
つだけが返される。
rdd.collectAsMap() Map{(1, 2),
(3, 6)
}
lookup(key)
指定されたキーに関連づけられたすべての値
を返す。
rdd.lookup(3) [4, 6]
ペア
RDD
には、この他にも
RDD
を保存するアクションが複数あります。それらについては、
5
で取り上げます。
4.5
データのーテニング（）
本章で最後に議論する
Spark
の機能は、データセットのノード間でのパーティショニングを制
御する方法です。分散プログラムでは、通信は非常にコストが高いので、ネットワークトラフィッ
クを最小限に抑えるようにデータを配置することによって、パフォーマンスを大幅に向上させるこ
とができます。単一ノードのプログラムにおいて、レコードのコレクションで適切なデータ構造を ...
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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.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
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.