[英]Unable to add elements to scala mutable list inside foreach loop
I am trying to add elements in a mutable scala list
as below.我正在尝试在
mutable scala list
添加元素,如下所示。 I am reading the values from a dataframe row by row, extracting out values of column with name "_title" and adding it to list.我正在逐行读取数据帧中的值,提取名称为“_title”的列的值并将其添加到列表中。 But when for loop is complete, the list is still enmpty.
但是当 for 循环完成时,列表仍然是空的。 this is the code:
这是代码:
import scala.collection.mutable.ListBuffer
val flatK = dfR.withColumn("UserValue", explode(col("UserValue")))
var colListA = new ListBuffer[String]()
// var colSet : List[String] = List()
for(i <- 0 until Integer.parseInt(dfR.count().toString)){
flatK.filter($"columnIndex" === i).foreach{
r=>
val columnName = r.getAs[Row]("UserValue").getAs[String]("_title")
// println(columnName)
colListA.append(columnName)
}
}
println(columnName)
actually prints the value I want to put inside my list. println(columnName)
实际上打印了我想放入列表中的值。 My dataframe dfR
looks like this:我的数据
dfR
如下所示:
+--------------------------------------------------------------+-----------+
|UserValue |columnIndex|
+--------------------------------------------------------------+-----------+
|[, last_mod_date, 2009-01-14T13:40:53] |0 |
|[, object_string, SOLIDS] |0 |
|[, last_mod_date, 2009-01-13T22:58:30] |1 |
|[, object_string, TORSO] |1 |
When I do当我做
colListA += "elements"
colListA += "adds"
I can see elements added.我可以看到添加的元素。 But not inside that
foreach
loop.但不在那个
foreach
循环中。 Can any one tell me what shall I try?谁能告诉我我该尝试什么? Basically, I expect colList to be populated with
last_mod_date
and object_string
.基本上,我希望 colList 填充
last_mod_date
和object_string
。
If you want to create a list from column of a dataframe dataframe.select("_title").collect().map(_(0).asInstanceOf[String]).toList
如果要从数据
dataframe.select("_title").collect().map(_(0).asInstanceOf[String]).toList
列创建列表
you can get the list of string of your column.您可以获取列的字符串列表。
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