November 2017
Intermediate to advanced
328 pages
6h 51m
Japanese
Content preview from 入門 PySpark ―PythonとJupyterで活用するSpark 2エコシステム
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3.4
DataFrame
の生成
39
これで RDD ができたので SparkSessionの
read.json
メソッド（ す なわ ち
s par k.rea d.jso n(...)
）
を使ってDataFrame に変換しましょう。また
.createOrReplaceTempView
メソッドを使って一時
テーブルも作成します。
Spark 1.x
では、同じことをするメソッドは
.registerTempTable
で すが 、こ れは
Spark 2.x
では非推奨とされました。
3.4.2
DataFrame
の生成
DataFrameを生成するコードは次のとおりです。
swimmersJSON = spark.read.json(stringJSONRDD)
3.4.3
一時テーブルの生成
一時テーブルを生成するコードは次のとおりです。
swimmersJSON.createOrReplaceTempView("swimmersJSON")
これまでの章で述べたとおり、RDD の操作の多くは変換であり、アクションの処理が呼ばれるまでは
実行されません。たとえば上のコードでは、
sc.parallelize
は変換であり、
spark.read.json
に
よって RDD から DataFrame への変換が行われる際に実行されます。注意が必要なのは、このコードの
ノートブックの画面（左下）では、
spark.read.json
の処理がある2番めのセルが実行されるまでは
Spark のジョブは実行されないというこ ...
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