Apache Spark，添加一个“CASE WHEN ... ELSE ..."；计算列到现有 DataFrame [英] Apache Spark, add an "CASE WHEN ... ELSE ..." calculated column to an existing DataFrame

问题描述

我正在尝试使用 Scala API 将CASE WHEN ... ELSE ..."计算列添加到现有 DataFrame.起始数据帧:

I'm trying to add an "CASE WHEN ... ELSE ..." calculated column to an existing DataFrame, using Scala APIs. Starting dataframe:

color
Red
Green
Blue

所需的数据框(SQL 语法:CASE WHEN color == Green THEN 1 ELSE 0 END AS bool):

Desired dataframe (SQL syntax: CASE WHEN color == Green THEN 1 ELSE 0 END AS bool):

color bool
Red   0
Green 1
Blue  0

我应该如何实现这个逻辑?

How should I implement this logic?

推荐答案

在即将发布的 SPARK 1.4.0 版本中(应该在接下来的几天内发布).您可以使用 when/otherwise 语法:

In the upcoming SPARK 1.4.0 release (should be released in the next couple of days). You can use the when/otherwise syntax:

// Create the dataframe
val df = Seq("Red", "Green", "Blue").map(Tuple1.apply).toDF("color")

// Use when/otherwise syntax
val df1 = df.withColumn("Green_Ind", when($"color" === "Green", 1).otherwise(0))

如果您使用的是 SPARK 1.3.0，您可以选择使用 UDF:

If you are using SPARK 1.3.0 you can chose to use a UDF:

// Define the UDF
val isGreen = udf((color: String) => {
  if (color == "Green") 1
  else 0
})
val df2 = df.withColumn("Green_Ind", isGreen($"color"))

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