What would be the idiomatic way to map this data? - scala

Question

I'm pretty new to Scala and while working I found the need to map some data found within a log file. The log file follows this format (values changed from original):
1343,37284.ab1-tbd,283
1344,37284.ab1-tbd,284
1345,37284.ab1-tbd,0
1346,28374.ab1-tbd,107
1347,28374.ab1-tbd,0
...
The first number is not important, but the number portion of the second field and the third field are what need to be mapped. I need the map to have keys that correspond to the number portion of the second field that map to a list of every 3rd field that follows it. That was a bad explanation, so as an example here is what I would need after parsing the above log:
{
37284 => { 283, 284, 0 }
28374 => { 107, 0 }
}
The solution I came up with is this:
val data = for (line <- Source fromFile "path/to/log" getLines) yield line.split(',')
val ls = data.toList
val keys = ls.map(_(1).split('.')(0).toInt)
val vals = ls.map(_(2).toInt)
val keys2vals = for {
(k, v) <- (keys zip vals).groupBy(_._1)
list = v.map(_._2)
} yield (k, list)
Is there a more idiomatic way to do this in Scala? This seems kinda awkward and convoluted to me. (When explaining, please assume little to no background knowledge of langauge features, etc.) Also, if later down the line I wanted to exclude the number zero from the mappings, how would I do so?
EDIT:
In addition, how would I similarly turn the data into the form:
{
{ 37284, { 283 ,284, 0 } }
{ 28374, { 107, 0 } }
}
i.e. a List[(Int, List[Int])]? (This form is for use with apache-spark's indexed rdds)

Answer 1

How about:
val assocList = for {
line <- Source.fromFile("path/to/log").getLines
Array(_, snd, thd) = line.split(',')
} yield (snd.split('.')(0).toInt, thd.toInt)
assocList.toList.groupBy(_._1).mapValues(_.map(_._2))
If you want a List[(Int, List[Int])], add .toList.

Answer 2

I might be tempted to write it in fewer lines (arguably clearer too) like this:
val l = List((1343,"37284.ab1-tbd",283),
(1344,"37284.ab1-tbd",284),
(1345,"37284.ab1-tbd",0),
(1346,"28374.ab1-tbd",107),
(1347,"28374.ab1-tbd",0))
// drop the unused data
val m = l.map(a => a._2.split('.')(0).toInt -> a._3)
// transform to Map of key -> matchedValues
m.groupBy(_._1) mapValues (_ map (_._2))
gives:
m: List[(Int, Int)] = List((37284,283), (37284,284), (37284,0), (28374,107), (28374,0))
res0: scala.collection.immutable.Map[Int,List[Int]] = Map(37284 -> List(283, 284, 0), 28374 -> List(107, 0))
"Also, if later down the line I wanted to exclude the number zero from the mappings, how would I do so?" - You could filter the initial list:
val m = l.filter(_._3 != 0).map(a => a._2.split('.')(0) -> a._3)
To convert to List[(Int, List[Int])] you just need to call .toList on the resulting Map.

Answer 3

val lines = io.Source.fromFile("path/to/log").getLines.toList
lines.map{x=>
val Array(_,second,_,fourth) = x.split("[,.]")
(second,fourth)
}.groupBy(_._1)
.mapValues(_.map(_._2))