PySpark:withColumn() 有两个条件和三个结果 [英] PySpark: withColumn() with two conditions and three outcomes

问题描述

我正在使用 Spark 和 PySpark.我正在尝试实现等效于以下伪代码的结果:

I am working with Spark and PySpark. I am trying to achieve the result equivalent to the following pseudocode:

df = df.withColumn('new_column', 
    IF fruit1 == fruit2 THEN 1, ELSE 0. IF fruit1 IS NULL OR fruit2 IS NULL 3.)

我正在尝试在 PySpark 中执行此操作，但我不确定语法.任何指针?我查看了 expr() 但无法让它工作.

I am trying to do this in PySpark but I'm not sure about the syntax. Any pointers? I looked into expr() but couldn't get it to work.

注意 df 是一个 pyspark.sql.dataframe.DataFrame.

推荐答案

有几种有效的方法可以实现这一点.让我们从必需的导入开始:

There are a few efficient ways to implement this. Let's start with required imports:

from pyspark.sql.functions import col, expr, when

你可以在 expr 中使用 Hive IF 函数:

You can use Hive IF function inside expr:

new_column_1 = expr(
    """IF(fruit1 IS NULL OR fruit2 IS NULL, 3, IF(fruit1 = fruit2, 1, 0))"""
)

或when + otherwise:

new_column_2 = when(
    col("fruit1").isNull() | col("fruit2").isNull(), 3
).when(col("fruit1") == col("fruit2"), 1).otherwise(0)

最后你可以使用以下技巧:

Finally you could use following trick:

from pyspark.sql.functions import coalesce, lit

new_column_3 = coalesce((col("fruit1") == col("fruit2")).cast("int"), lit(3))

使用示例数据:

df = sc.parallelize([
    ("orange", "apple"), ("kiwi", None), (None, "banana"), 
    ("mango", "mango"), (None, None)
]).toDF(["fruit1", "fruit2"])

您可以按如下方式使用它:

you can use this as follows:

(df
    .withColumn("new_column_1", new_column_1)
    .withColumn("new_column_2", new_column_2)
    .withColumn("new_column_3", new_column_3))

结果是:

+------+------+------------+------------+------------+
|fruit1|fruit2|new_column_1|new_column_2|new_column_3|
+------+------+------------+------------+------------+
|orange| apple|           0|           0|           0|
|  kiwi|  null|           3|           3|           3|
|  null|banana|           3|           3|           3|
| mango| mango|           1|           1|           1|
|  null|  null|           3|           3|           3|
+------+------+------------+------------+------------+

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