I have an array like this
(20140101,20140102,20140103,20140104,20140105,20140106,20140107,20140108)
I want to create a map from this by prefixing each value with "s3://" and concatenating three values with a comma.
Output:
val params = Map("1"-> "s3://20140101,s3://20140102,s3://20140103","2"-> "s3://20140104,s3://20140105,s3://20140106","3"->"s3://20140107,s3://20140108")
I'm a beginner and kindly request some thoughts here.
This returns a Map[Int, Array[String]]. If you really want the values as a String, then use mapValues(_.mkString(",")) on the result.
scala> val xs = Array(20140101,20140102,20140103,20140104,20140105,20140106,20140107,20140108)
xs: Array[Int] = Array(20140101, 20140102, 20140103, 20140104, 20140105, 20140106, 20140107, 20140108)
scala> xs.map(x => "s3://" + x).grouped(3).zipWithIndex.map(t => (t._2, t._1)).toMap
res16: scala.collection.immutable.Map[Int,Array[String]] = Map(0 -> Array(s3://20140101, s3://20140102, s3://20140103), 1 -> Array(s3://20140104, s3://20140105, s3://20140106), 2 -> Array(s3://20140107, s3://20140108))
I think this will do what you want:
val array = Array(20140101, 20140102, 20140103, 20140104, 20140105, 20140106, 20140107, 20140108)
val result = array.
sliding(3, 3). // this selects 3 elements at a time and steps 3 elements at a time
zipWithIndex. // this adds an index to the 3 elements
map({ case (arr, i) => (i + 1).toString -> arr.map(a => "s3://" + a.toString).mkString(",")}). // this makes a tuple and concats the array elements
toMap // this transforms the Array of tuples into a map
println(result)
//prints Map(1 -> s3://20140101,s3://20140102,s3://20140103, 2 -> s3://20140104,s3://20140105,s3://20140106, 3 -> s3://20140107,s3://20140108)
.view before all the operations so that new arrays won't be created every time
view is a strange beast, and it's implementation makes me not want to use it as it seems non-deterministic. With that said, I tried it and got this error Exception in thread "main" java.lang.ClassCastException: scala.collection.SeqViewLike$$anon$1 cannot be cast to scala.collection.mutable.IndexedSeqViewtoList works, but doesn't that defeat the purpose of using the view?scala.collection.mutable.WrappedArray. It only costs an instantiation, O(1). Just define val array as val array: IndexedSeq[Int]. It worked in my REPL :)Just another variation, this time avoiding zipWithIndex and the key value swap
val xs = Array(20140101,20140102,20140103,20140104,20140105,20140106,20140107,20140108)
Iterator.from(0).zip{xs.grouped(3).map{"s://"+ _.mkString(",")}}.toMap
You can convert it to a tuple then turn that tuple into a map. Like this:
val xs = Array(20140101,20140102,20140103,20140104,20140105,20140106,20140107,20140108)
val xsMap = ((1 to (xs.length + 1))
zip xs.map(valueAtIndex => "s://" + valueAtIndex)).toMap
This won't be particularly fast but it is simple and makes sense. Note: I only tested this will the new scala3 compiler: dotty. The scala version I am using is 3.0.1.
