August 2015
Intermediate to advanced
312 pages
7h 28m
Japanese
Content preview from 初めてのSpark
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174
9 章 Spark SQL
最後に登場している構造体は、
Spark SQL
では単に
Row
として表現されます。この型は、他の
型とネストすることができます。例えば、構造体の配列や、構造体を含むマップを作ることができ
ます。
Row
オブジェクトの処理
Row
オブジェクトは
SchemaRDD
内のレコードを表現するもので、固定長のフィールドの配列
にすぎません。
Scala/Java
では、
Row
オブジェクトにはいくつもの
getter
関数があり、渡したイ
ンデックスに対応するフィールドの値を取得できます。標準的な
getter
である
get
（
Scala
の場
合は
apply
）は、列の番号を引数として取り、
Object
型（
Scala
では
Any
）の値を返します。この
値を適切な型にキャストするのは、プログラマーの役目です。
Boolean
、
Byte
、
Double
、
Float
、
Int
、
Long
、
Short
、
String
といった型に対しては、
getType()
メソッドが用意されており、その
型の値が返されます。例えば、
getString(0)
は、
0
番目のフィールドの値を文字列として返しま
す。
9-12
および
9-13
をご覧ください。
9-12
SchemaRDD
topTweets
text
Scala
val topTweetText = topTweets.map(row => row.getString(0))
9-13
SchemaRDD
topT
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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.