在Spark Dataframe中将字符串转换为日期

问题描述：

我有一个带有2个StringType字段的数据框(df1).

I have a dataframe (df1) with 2 StringType fields.

Field1(StringType)值-X

Field1 (StringType) Value-X

Field2(StringType)值-20180101

Field2 (StringType) value-20180101

我要做的就是从df1中创建另一个具有2个字段的数据框(df2)-

All I am trying to do is create another dataframe (df2) from df1 with 2 fields-

Field1(StringType)值-X

Field1 (StringType) Value-X

Field2(日期类型)值-2018-01-01

Field2 (Date Type) Value-2018-01-01

我正在使用下面的代码-

I am using the below code-

df2=df1.select(
     col("field1").alias("f1"),
     unix_timestamp(col("field2"),"yyyyMMdd").alias("f2")
)

df2.show

df2.printSchema

对于此字段2，我尝试了多种操作-unix_timestamp，from_unixtimestamp，to_date，cast(date)，但没有任何作用

For this field 2, I tried multiple things - unix_timestamp , from_unixtimestamp, to_date, cast("date") but nothing worked

我需要以下模式作为输出:

I need the following schema as output:

df2.printSchema
|-- f1: string (nullable = false)
|-- f2: date (nullable = false)

我正在使用Spark 2.1

I'm using Spark 2.1

答

to_date似乎可以很好地满足您的需求:

to_date seems to work fine for what you need:

import org.apache.spark.sql.functions._

val df1 = Seq( ("X", "20180101"), ("Y", "20180406") ).toDF("c1", "c2")

val df2 = df1.withColumn("c2", to_date($"c2", "yyyyMMdd"))

df2.show
// +---+----------+
// | c1|        c2|
// +---+----------+
// |  X|2018-01-01|
// |  Y|2018-04-06|
// +---+----------+

df2.printSchema
// root
//  |-- c1: string (nullable = true)
//  |-- c2: date (nullable = true)

[更新]

对于Spark 2.1或更低版本，to_date不会将格式字符串作为参数，因此需要使用例如regexp_replace的显式字符串格式设置为标准yyyy-MM-dd格式:

For Spark 2.1 or prior, to_date doesn't take format string as a parameter, hence explicit string formatting to the standard yyyy-MM-dd format using, say, regexp_replace is needed:

val df2 = df1.withColumn(
  "c2", to_date(regexp_replace($"c2", "(\\d{4})(\\d{2})(\\d{2})", "$1-$2-$3"))
)

在Spark Dataframe中将字符串转换为日期

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