Sorting 2D String array in Scala

Question

Hi I'm trying to sort a matrix by a column in alphabetical order

I tried with this: It's just a bubblesort that I tried out var artists2=Array.ofDimString// Artist Name,Year

var compare=0
var aux2=""
for(i <- 0 to 99){
        for(j <- 0 to 993){
          compare = artists(j)(0).compareTo(artists(j+1)(0))
      if (compare < 0)  { //a is smaller  b>a
        aux2=artists(j)(0)
                artists(j)(0)=artists(j+1)(0)
                artists(j+1)(0)=aux2

                aux2=artists(j)(1)
                artists(j)(1)=artists(j+1)(1)
                artists(j+1)(1)=aux2
      }  
        }
}
println(artists.map(_.mkString(" ")).mkString("\n"))

But I get a null pointer Exception I know this is not suposed to work with string so if you have any suggestions please let me know my matrix has tu colums artists and years I want to sort it out by the artists column but still conserve each artist year

Siyual · Accepted Answer · 2015-12-17 18:59:58Z

2

If you want to sort an array you can simply call the sortBy method in Scala.

scala> val artists = Array(("ArtistA",1987), ("ArtistC", 1545), ("ArtistB", 2014))
artists: Array[(String, Int)] = Array((ArtistA,1987), (ArtistC,1545), (ArtistB,2014))

scala> artists.sortBy(_._1)
Array[(String, Int)] = Array((ArtistA,1987), (ArtistB,2014), (ArtistC,1545))

Here is the case where your data are not in an Array[(String, Int)] type but in a 2D Array. Note that unlike tuples, 2D Arrays cannot support having multiple types (you can but they lose their type to 'Any'). So the Array will be of type Array[Array[String]].

val d2 = Array(Array("ArtistA","ArtistC","ArtistB"), Array("1987", "1545", "2014"))
d2: Array[Array[String]] = Array(Array(ArtistA, ArtistC, ArtistB), Array(1987, 1545, 2014))

val sorted = d2(0).zip(d2(1)).sortBy(_._1).unzip  
sorted: (Array[String], Array[String]) = (Array(ArtistA, ArtistB, ArtistC),Array(1987, 2014, 1545))

The idea here is that you first break the 2D array using zip to create an array of tuples. Next you sort it, and finally you unzip it.

edited Dec 17, 2015 at 18:59

Siyual

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answered Dec 17, 2015 at 17:15

marios

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3 Comments

ativg Over a year ago

I get this error

not enough arguments for method sortBy: (implicit ord: scala.math.Ordering[B])Array[Array[String]]. Unspecified value parameter ord.

marios Over a year ago

Can you give me an example input data? Similar to what I do here with 'artists'?

ativg Over a year ago

"Korn","1987" I want to sort it out by artists alphabeticallly, the two fields are strings

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