[英]scala - Spark : How to union all dataframe in loop
有沒有辦法在循環中獲取聯合數據幀的數據幀?
這是一個示例代碼:
var fruits = List(
"apple"
,"orange"
,"melon"
)
for (x <- fruits){
var df = Seq(("aaa","bbb",x)).toDF("aCol","bCol","name")
}
我想獲得一些這樣的:
aCol | bCol | fruitsName
aaa,bbb,apple
aaa,bbb,orange
aaa,bbb,melon
再次感謝
您可以創建一個DataFrame
序列,然后使用reduce
:
val results = fruits.
map(fruit => Seq(("aaa", "bbb", fruit)).toDF("aCol","bCol","name")).
reduce(_.union(_))
results.show()
Steffen Schmitz 的回答是我認為最簡潔的回答。 如果您正在尋找更多自定義(字段類型等),以下是更詳細的答案:
import org.apache.spark.sql.types.{StructType, StructField, StringType}
import org.apache.spark.sql.Row
//initialize DF
val schema = StructType(
StructField("aCol", StringType, true) ::
StructField("bCol", StringType, true) ::
StructField("name", StringType, true) :: Nil)
var initialDF = spark.createDataFrame(sc.emptyRDD[Row], schema)
//list to iterate through
var fruits = List(
"apple"
,"orange"
,"melon"
)
for (x <- fruits) {
//union returns a new dataset
initialDF = initialDF.union(Seq(("aaa", "bbb", x)).toDF)
}
//initialDF.show()
參考:
如果您有不同/多個數據幀,您可以使用以下代碼,這很有效。
val newDFs = Seq(DF1,DF2,DF3)
newDFs.reduce(_ union _)
在 for 循環中:
val fruits = List("apple", "orange", "melon")
( for(f <- fruits) yield ("aaa", "bbb", f) ).toDF("aCol", "bCol", "name")
嗯......我認為你的問題有點誤導。
根據我對您嘗試做的任何事情的有限理解,您應該遵循以下步驟,
val fruits = List(
"apple",
"orange",
"melon"
)
val df = fruits
.map(x => ("aaa", "bbb", x))
.toDF("aCol", "bCol", "name")
這應該就足夠了。
您可以先創建一個序列,然后使用toDF
創建Dataframe
。
scala> var dseq : Seq[(String,String,String)] = Seq[(String,String,String)]()
dseq: Seq[(String, String, String)] = List()
scala> for ( x <- fruits){
| dseq = dseq :+ ("aaa","bbb",x)
| }
scala> dseq
res2: Seq[(String, String, String)] = List((aaa,bbb,apple), (aaa,bbb,orange), (aaa,bbb,melon))
scala> val df = dseq.toDF("aCol","bCol","name")
df: org.apache.spark.sql.DataFrame = [aCol: string, bCol: string, name: string]
scala> df.show
+----+----+------+
|aCol|bCol| name|
+----+----+------+
| aaa| bbb| apple|
| aaa| bbb|orange|
| aaa| bbb| melon|
+----+----+------+
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