问题
I have List[N] like below
val check = List ("a","b","c","d")
where N can be any number of elements.
I have a dataframe with only column called "value". Based on the contents of value i need to create N columns with column names as elements in the list and column contents as substring(x,y)
I have tried all possible ways, like withColumn, selectExpr, nothing works.
Please consider substring(X,Y) where X and Y as some numbers based on some metadata
Below are my different codes which I tried, but none worked,
val df = sqlContext.read.text("xxxxx")
val coder: (String => String) = (arg: String) => {
val param = "NULL"
if (arg.length() > Y )
arg.substring(X,Y)
else
val sqlfunc = udf(coder)
val check = List ("a","b","c","d")
for (name <- check){val testDF2 = df.withColumn(name, sqlfunc(df("value")))}
testDF2 has only last column d and other columns such as a,b,c are not added in table
var z:Array[String] = new Array[String](check.size)
var i=0
for ( x <- check ) {
if ( (i+1) == check.size) {
z(i) = s""""substring(a.value,X,Y) as $x""""
i = i+1}
else{
z(i) = s""""substring(a.value,X,Y) as $x","""
i = i+1}}
val zz = z.mkString(" ")
df.alias("a").selectExpr(s"$zz").show()
This throws error
Please help how to add columns in DF dynamically with column names as elements in List
I am expecting an Df like below
-----------------------------
Value| a | b | c | d | .... N
-----------------------------
|xxx|xxx|xxx|xxx|xxx|xxxxxx-
|xxx|xxx|xxx|xxx|xxx|xxxxxx-
|xxx|xxx|xxx|xxx|xxx|xxxxxx-
-----------------------------
回答1:
you can dynamically add columns from your list using for instance this answer by user6910411 to a similar question (see her/his full answer for more possibilities):
val newDF = check.foldLeft(<yourdf>)((df, name) => df.withColumn(name,<yourUDF>$"value"))
来源：https://stackoverflow.com/questions/42761328/add-columns-in-dataframes-dynamically-with-column-names-as-elements-in-list