apache-spark - 如何在spark中连接数据框中的字符串和列？

Question

我有今天的日期作为字符串。我需要将它与作为数据帧中的列存在的时间值连接起来。

当我尝试这个时，我得到 String Index out of bounds异常(exception)。

我的代码:

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

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

预期输出:

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

Answer 1

**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|
|+-------------------+