scala DataFrame 错误：“重载的方法值选择与替代”
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DataFrame error: “overloaded method value select with alternatives”
提问by Jason.Liu
I tried to create a new dataframe by select hour+minute/60 and other columns from a dataframe as follows:
我尝试通过从数据框中选择小时+分钟/60 和其他列来创建一个新的数据框，如下所示：
val logon11 = logon1.select("User","PC","Year","Month","Day","Hour","Minute",$"Hour"+$"Minute"/60)
I got the error below:
我收到以下错误：
<console>:38: error: overloaded method value select with alternatives:
(col: String,cols: String*)org.apache.spark.sql.DataFrame <and>
(cols: org.apache.spark.sql.Column*)org.apache.spark.sql.DataFrame
cannot be applied to (String, String, String, String, String, String, String,org.apache.spark.sql.Colum)
...
Maybe I have known the reason is that I cannot get a DataFrame with these types using "select" at the same time. Then how can I get such dataframe?
也许我已经知道原因是我无法同时使用“select”获得这些类型的 DataFrame。那我怎样才能得到这样的数据框呢？
回答by avr
DF's selectmethod takes arguments of type either all Strings or all org.apache.spark.sql.Columns but doesn't take mix of both.
DF 的select方法采用 all Strings 或 all org.apache.spark.sql.Columns类型的参数，但不混合使用两者。
In your case you are passing both Stringand Columntype parameters to selectmethod.
在您的情况下，您将String和Column类型参数传递给select方法。
val logon11 = logon1.select($"User",$"PC",$"Year",$"Month",$"Day",$"Hour",$"Minute",$"Hour"+$"Minute"/60 as "total_hours")
Hope it helps!
希望能帮助到你！
回答by Prasad Khode
you can use withColumncreate a new column from existing columns or based on some conditions like below
您可以使用withColumn从现有列或基于以下条件创建新列
val logon1 = Seq(("User1","PC1",2017,2,12,12,10)).toDF("User","PC","Year","Month","Day","Hour","Minute")
val logon11 = logon1.withColumn("new_col", $"Hour"+$"Minute"/60)
logon11.printSchema()
logon11.show
output:
输出：
root
|-- User: string (nullable = true)
|-- PC: string (nullable = true)
|-- Year: integer (nullable = false)
|-- Month: integer (nullable = false)
|-- Day: integer (nullable = false)
|-- Hour: integer (nullable = false)
|-- Minute: integer (nullable = false)
|-- new_col: double (nullable = true)
+-----+---+----+-----+---+----+------+------------------+
| User| PC|Year|Month|Day|Hour|Minute| new_col|
+-----+---+----+-----+---+----+------+------------------+
|User1|PC1|2017| 2| 12| 12| 10|12.166666666666666|
+-----+---+----+-----+---+----+------+------------------+
