如何将字符串数组的列转换为字符串? [英] How to convert column of arrays of strings to strings?

问题描述

我有一列，它的类型是 array <火花表中的字符串 >.我正在使用 SQL 来查询这些火花表.我想转换 array <string > 到 string.

I have a column, which is of type array < string > in spark tables. I am using SQL to query these spark tables. I wanted to convert the array < string > into string.

使用以下语法时:

select cast(rate_plan_code  as string) as new_rate_plan  from
customer_activity_searches group by rate_plan_code

rate_plan_code 列具有以下值:

["AAA","RACK","SMOBIX","SMOBPX"] 
["LPCT","RACK"]
["LFTIN","RACK","SMOBIX","SMOBPX"]
["LTGD","RACK"] 
["RACK","LEARLI","NHDP","LADV","LADV2"]

在 new_rate_plan 列中填充以下内容:

following are populated in the new_rate_plan column:

org.apache.spark.sql.catalyst.expressions.UnsafeArrayData@e4273d9f
org.apache.spark.sql.catalyst.expressions.UnsafeArrayData@c1ade2ff
org.apache.spark.sql.catalyst.expressions.UnsafeArrayData@4f378397
org.apache.spark.sql.catalyst.expressions.UnsafeArrayData@d1c81377
org.apache.spark.sql.catalyst.expressions.UnsafeArrayData@552f3317

当我将 decimal 转换为 int 或 int 到 double 时，

Cast 似乎有效，但在这个案例.很好奇为什么演员不在这里工作.非常感谢您的帮助.

Cast seem to work when I am converting decimal to int or int to double, but not in this case. Curious why the cast is not not working here. Greatly appreciate your help.

推荐答案

在 Spark 2.1+ 中，您可以使用以下方法对单个 Array 列中的值进行串联:

In Spark 2.1+ to do the concatenation of the values in a single Array column you can use the following:

1. concat_ws 标准函数
2. map 运算符
3. 用户定义函数 (UDF)

concat_ws 标准函数

使用 concat_ws 函数.

concat_ws(sep: String, exprs: Column*): Column 使用给定的分隔符将多个输入字符串列连接成一个字符串列.

concat_ws(sep: String, exprs: Column*): Column Concatenates multiple input string columns together into a single string column, using the given separator.

val solution = words.withColumn("codes", concat_ws(" ", $"rate_plan_code"))
scala> solution.show
+--------------+-----------+
|         words|      codes|
+--------------+-----------+
|[hello, world]|hello world|
+--------------+-----------+

地图操作员

使用 map 操作符可以完全控制应该转型什么以及如何转型.

map Operator

Use map operator to have full control of what and how should be transformed.

ma​​p[U](func: (T) ⇒ U): Dataset[U] 返回一个新的 Dataset，其中包含将 func 应用于每个元素的结果.

map[U](func: (T) ⇒ U): Dataset[U] Returns a new Dataset that contains the result of applying func to each element.

scala> codes.show(false)
+---+---------------------------+
|id |rate_plan_code             |
+---+---------------------------+
|0  |[AAA, RACK, SMOBIX, SMOBPX]|
+---+---------------------------+

val codesAsSingleString = codes.as[(Long, Array[String])]
  .map { case (id, codes) => (id, codes.mkString(", ")) }
  .toDF("id", "codes")

scala> codesAsSingleString.show(false)
+---+-------------------------+
|id |codes                    |
+---+-------------------------+
|0  |AAA, RACK, SMOBIX, SMOBPX|
+---+-------------------------+

scala> codesAsSingleString.printSchema
root
 |-- id: long (nullable = false)
 |-- codes: string (nullable = true)

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