Apache spark 如何在spark中连接数据帧中的字符串和列？

我把今天的日期作为一个字符串。我需要将它与一个时间值连接起来，该时间值在数据帧中作为列显示

当我尝试此操作时，我得到

字符串索引超出范围

异常

我的代码：

val todaydate = LocalDate.now().toString()
println(todaydate)  // o/p: 2016-12-10

val todayrec_cutoff = todaydate + (" ") + df.col("colname")

预期产出：

2016-12-10 05:00 
2016-12-10 22:30

---

你可以像下面这样做

import java.time.LocalDate

val df = Seq(("05:00"), ("22:30")).toDF("time")
df.show
val todaydate = LocalDate.now().toString()
val df2 = df.select(concat(lit(todaydate+ " "),df.col("time"))).toDF("datetime");
df2.show

这会给你

+----------------+
|        datetime|
+----------------+
|2016-12-10 05:00|
|2016-12-10 22:30|
+----------------+

---

在Python 2.7中，lit是否不可用？

**Please refer to below Scala code for string concat in prefix and postfix way.**


import org.apache.spark.sql.functions._
val empDF =  MongoSpark.load(spark, readConfig) //dataframe empDF is loaded from Mongo DB using MongoSpark 

val prefixVal= "PrefixArkay " //variable string
val postfixVal= " PostfixArkay"

//Prefix
val finalPreDF = ipDF.withColumn("EMP", concat(lit(prefix),empDF.col("EMP")) )
println("finalPreDF.show-> " + finalPreDF.show())

//Output will be as below
+-------------------+
|                EMP|
+-------------------+
|PrefixArkay DineshS|
|+------------------+


val finalPostDF = ipDF.withColumn("EMP", concat(empDF.col("EMP"),lit(postfixVal)) )
println("finalPostDF.show-> " + finalPostDF .show())

//Output will be as below
+--------------------+
|                 EMP|
+--------------------+
|DineshS PostfixArkay|
|+-------------------+