scala - Why is join not possible after show operator? -


the following code works fine until add show after agg. why show not possible?

 val temptableb = tableb.groupby("idb")   .agg(first("numb").as("numb")) //when add .show here, doesn't work   tablea.join(temptableb, $"ida" === $"idb", "inner")  .drop("ida", "numa").show

the error says:

error: overloaded method value join alternatives:   (right: org.apache.spark.sql.dataset[_],joinexprs: org.apache.spark.sql.column,jointype: string)org.apache.spark.sql.dataframe <and>   (right: org.apache.spark.sql.dataset[_],usingcolumns: seq[string],jointype: string)org.apache.spark.sql.dataframe  cannot applied (unit, org.apache.spark.sql.column, string)               tablea.join(temptableb, $"ida" === $"idb", "inner")                      ^

why behaving way?

.show() function with, call in scala, side-effect. prints stdout , returns unit(), println

example: 

val  = array(1,2,3).foreach(println) a: unit = ()

in scala, can assume function , return something. in case, unit() being returned , that's what's getting stored in temptableb.


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