Spark 等效于 IF Then ELSE [英] Spark Equivalent of IF Then ELSE

问题描述

我早些时候在这里看到过这个问题，我从中吸取了教训.但是，我不确定为什么我觉得它应该可以工作时会出错.

I have seen this question earlier here and I have took lessons from that. However I am not sure why I am getting an error when I feel it should work.

我想通过一些规则在现有 Spark DataFrame 中创建一个新列.这是我写的.iris_spark 是具有三个不同类别的分类变量 iris_spark 的数据框.

I want to create a new column in existing Spark DataFrame by some rules. Here is what I wrote. iris_spark is the data frame with a categorical variable iris_spark with three distinct categories.

from pyspark.sql import functions as F

iris_spark_df = iris_spark.withColumn(
    "Class", 
   F.when(iris_spark.iris_class == 'Iris-setosa', 0, F.when(iris_spark.iris_class == 'Iris-versicolor',1)).otherwise(2))

抛出以下错误.

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-157-21818c7dc060> in <module>()
----> 1 iris_spark_df=iris_spark.withColumn("Class",F.when(iris_spark.iris_class=='Iris-setosa',0,F.when(iris_spark.iris_class=='Iris-versicolor',1)))

TypeError: when() takes exactly 2 arguments (3 given)


---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-157-21818c7dc060> in <module>()
----> 1 iris_spark_df=iris_spark.withColumn("Class",F.when(iris_spark.iris_class=='Iris-setosa',0,F.when(iris_spark.iris_class=='Iris-versicolor',1)))

TypeError: when() takes exactly 2 arguments (3 given)

知道为什么吗?

推荐答案

正确的结构是:

(when(col("iris_class") == 'Iris-setosa', 0)
.when(col("iris_class") == 'Iris-versicolor', 1)
.otherwise(2))

相当于

CASE 
    WHEN (iris_class = 'Iris-setosa') THEN 0
    WHEN (iris_class = 'Iris-versicolor') THEN 1 
    ELSE 2
END

或:

(when(col("iris_class") == 'Iris-setosa', 0)
    .otherwise(when(col("iris_class") == 'Iris-versicolor', 1)
        .otherwise(2)))

相当于:

CASE WHEN (iris_class = 'Iris-setosa') THEN 0 
     ELSE CASE WHEN (iris_class = 'Iris-versicolor') THEN 1 
               ELSE 2 
          END 
END

一般语法:

when(condition, value).when(...)

或

when(condition, value).otherwise(...)

你可能混淆了 Hive IF 条件:

You probably mixed up things with Hive IF conditional:

IF(condition, if-true, if-false)

只能在支持 Hive 的原始 SQL 中使用.

which can be used only in raw SQL with Hive support.

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