Given that this example:
val myList = List("age=21", "name=xyz", "profession=Tester", "city=cuba", "age=43", "name=abc", "profession=Programmer", "city=wellington")
val myMap = myList.map(text => text.split("=")).map(a => (a(0) -> a(1))).toMap
works fine, returning:
myList: List[String] = List(age=21, name=xyz, profession=Tester, city=cuba, age=43, name=abc, profession=Programmer, city=wellington)
myMap: scala.collection.immutable.Map[String,String] = Map(age -> 43, name -> abc, profession -> Programmer, city -> wellington)
I am wondering why the following which is just N sets of values:
val myList = List("age=21", "name=xyz", "profession=Tester", "city=cuba", "age=43", "name=abc", "profession=Programmer", "city=Sydney")
val myMap = myList.grouped(4).toList.map(text => text.split("=")).map(a => (a(0) -> a(1))).toMap
generates the error, and how to solve:
notebook:9: error: value split is not a member of List[String]
val myMap = myList.grouped(4).toList.map(text => text.split("=")).map(a => (a(0) -> a(1))).toMap
I must be missing something elementary here.
myList.grouped(4).toList returns a nested list – List[List[String]].
To transform the grouped sublists into Maps:
val myMap = myList.grouped(4).toList.
map(_.map(_.split("=")).map(a => (a(0) -> a(1))).toMap)
// myMap: List[scala.collection.immutable.Map[String,String]] = List(
// Map(age -> 21, name -> xyz, profession -> Tester, city -> cuba),
// Map(age -> 43, name -> abc, profession -> Programmer, city -> Sydney)
// )
Related
I have a Scala List of Map[String, String] like this:
val data: List[Map[String, String]] = List(Map("key" -> "123", "fname" -> "Alice", "lname" -> "Baker"), Map("key" -> "456", "fname" -> "Bob", "lname" -> "Lotts"))
I want to transform this to a List like this: List(Map(id -> 123, name -> Alice Baker), Map(id -> 456, name -> Bob Lotts)). Basically, I need to change the key to id and concatenate the fname and lname to name.
I tried the below code. It works, but I am sure there should be a better way of doing this. Can anyone please suggest?
val modData: List[Map[String, String]] = data.map(d => Map("id" -> d.getOrElse("key", ""), "name" -> s"${d.getOrElse("fname", "")} ${d.getOrElse("lname", "")}"))
I would do it in steps, and use default for the map to make it more readable:
val keys = Seq("key", "fname", "lname")
list.iterator
.map(_.withDefault(_ => ""))
.map(keys.map)
.collect { case Seq(id, fname, lname) => Map("id" -> id, "name" -> s"$fname $lname") }
.toList
I am using Scala's for comprehension to produce a modified facetFilter. If a value in facetFilter doesn't exist in allFacets, it should be filtered out. Currently, the newFacetFilter doesn't filter at all.
val allFacets = Map(
"band_material" -> Map("Rubber" -> 11),
"dial_color" -> Map("Ivory" -> 68, "Salmon"-> 3))
val facetFilter =
Map("band_material" -> List("Yellow Gold Plated", "Rubber"),
"dial_color" -> List("Ivory"))
val newFacetFilter =
for {
(k,v) <- allFacets
(facetName, facetArr) <- facetFilter
aFacet <- facetArr
if k != facetName || !v.contains(aFacet)
} yield (facetName -> facetArr)
Current Output of newFacetFilter:
Map("band_material" -> List("Yellow Gold Plated", "Rubber"), "dial_color" -> List("Ivory"))
Expected Output of newFacetFilter:
Map("band_material" -> List("Rubber"), "dial_color" -> List("Ivory"))
See this fiddle
Try this:
val newFacetFilter =
for ((k,vs) <- facetFilter)
yield (k, vs filter allFacets(k).contains)
Output:
Map(band_material -> List(Rubber), dial_color -> List(Ivory))
OK, if we are done with edits, I think this is what you want...
val allFacets = Map(
"band_material" -> Map(
"Rubber" -> 11
),
"dial_color" -> Map(
"Ivory" -> 68,
"Salmon"-> 3
)
)
val facetFilter = Map(
"band_material" -> List("Yellow Gold Plated", "Rubber"),
"dial_color" -> List("Ivory"),
"case_material" -> List(),
"movement" -> List(),
"price_range" -> List(),
"gender" -> List()
)
val newFacetFilter = for {
(facetName, facetArr) <- facetFilter
(k,v) <- allFacets
if k == facetName
} yield (facetName, facetArr intersect v.keys.toList)
We simply iterate both maps and when we have the same keys, we intersect the two lists.
Edit: There is a more efficient way, using the Map's get function instead of just iterating everything and ignoring non-matches.
val newFacetFilter = facetFilter.flatMap {
case (n, fs) =>
allFacets.get(n).map(n -> _.keys.toList.intersect(fs))
}
So we take each facetFilter entry ((n, fs)), check allFacets for n, then intersect the optional result with our list fs. If n did not exist, we propagate None and it is flattened out by flatMap.
I have an immutable map from which I wish to change a single element and then return another immutable map. Am I stuck with copying all elements twice?
val inmap = Map('a'->1,'b'->2)
import collection.mutable
val mmap = mutable.Map(inmap.toList:_*)
mmap('b')= 3
val mmap2 = Map(mmap.toList:_*)
mmap2: scala.collection.immutable.Map[Char,Int] = Map(b -> 3, a -> 1)
Just wondering if that were the 'required' price for immutability on the 'frontiers' of our methods.
You could use the updated method:
scala> val inmap = Map('a' -> 1, 'b' -> 2)
inmap: scala.collection.immutable.Map[Char,Int] = Map(a -> 1, b -> 2)
scala> val updated = inmap.updated('b', 3)
updated: scala.collection.immutable.Map[Char,Int] = Map(a -> 1, b -> 3)
API doc for Map: look to the updated method.
here is my data :
doc1: (Does,1) (just,-1) (what,0) (was,1) (needed,1) (to,0) (charge,1) (the,0) (Macbook,1)
doc2: (Pro,1) (G4,-1) (13inch,0) (laptop,1)
doc3: (Only,1) (beef,0) (was,1) (it,0) (no,-1) (longer,0) (lights,-1) (up,0) (the,-1)
etc...
and i want to extract words and values and then store them in two separated matrices , matrix_1 is (docID words) and matrix_2 is (docID values) ;
input.txt
=========
doc1: (Does,1) (just,-1) (what,0) (was,1) (needed,1) (to,0) (charge,1) (the,0) (Macbook,1)
doc2: (Pro,1) (G4,-1) (13inch,0) (laptop,1)
doc3: (Only,1) (beef,0) (was,1) (it,0) (no,-1) (longer,0) (lights,-1) (up,0) (the,-1)
val inputText = sc.textFile("input.txt")
var digested = input.map(line => line.split(":"))
.map(row => row(0) -> row(1).trim.split(" "))
.map(row => row._1 -> row._2.map(_.stripPrefix("(").stripSuffix(")").trim.split(",")))
var matrix_1 = digested.map(row => row._1 -> row._2.map( a => a(0)))
var matrix_2 = digested.map(row => row._1 -> row._2.map( a => a(1)))
gives:
List(
(doc1 -> Does,just,what,was,needed,to,charge,the,Macbook),
(doc2 -> Pro,G4,13inch,laptop),
(doc3 -> Only,beef,was,it,no,longer,lights,up,the)
)
List(
(doc1 -> 1,-1,0,1,1,0,1,0,1),
(doc2 -> 1,-1,0,1),
(doc3 -> 1,0,1,0,-1,0,-1,0,-1)
)
I want to turn this String:
"1:a|2:b|3:c"
into this:
Map(1 -> "a", 2 -> "b", 3 -> "c")
I have a procedural method that works, but it seems there ought to be a more functional approach.
val a = [YOUR STRING]
a.split('|').map(_.split(':')).map(a => (a(0) -> a(1))).toMap
val s = "1:a|2:b|3:c"
"(\\d+)\\:(\\w+)".r.findAllMatchIn(s).map( m => (m.group(1).toInt -> m.group(2)) ).toMap