Scala 2D array sorting by specified column

Question

Given any 2D array, e.g,

val in = Array( Array(59, 45, 32), 
                Array(20, 88, 5), 
                Array(49, 72, 89))

would like to sort it by the third column, so that

val out = Array( Array(20, 88, 5),
                 Array(59, 45, 32),                       
                 Array(49, 72, 89))

Many Thanks.

serejja · Accepted Answer · 2014-04-07 13:02:29Z

7

This should work, but will fail if your arrays are of size less than 3:

scala> in.sortBy(_(2))

Output:

res0: Array[Array[Int]] = Array(Array(20, 88, 5), Array(59, 45, 32), Array(49, 72, 89))

You may also make this fail-safe like this:

in.sortBy {
  case arr @ Array(_) if arr.size >= 3 => arr(2)
  case arr => Int.MaxValue // or any other value. Using MaxValue will make the invalid arrays be last ones
}

edited Apr 7, 2014 at 13:02

answered Apr 7, 2014 at 12:50

serejja

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2 Comments

Eastsun Over a year ago

Your second solution can write as scala> in.sortBy { case Array(_, _, x, _*) => x; case _ => Int.MaxValue }

serejja Over a year ago

Thanks. I think there are several ways to do the same thing and I just picked the first one I came to :)

Michael · Accepted Answer · 2014-04-07 12:52:38Z

1

in.sortWith(_(2) < _(2))

will sort the array, using the third element of the Array.

answered Apr 7, 2014 at 12:52

Michael

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Comments

Haimei · Accepted Answer · 2014-11-11 16:51:40Z

If your array is Array[Array[Int]], you just need to use yourArray.sortBy(_(3)). 3 is your field index, which you want to order according to this column.

But, if your array is not Array[Array[Int]], you can't use sortBy directly. You'd better to use Sorting which is imported from scala.util.Sorting

Here is my code.

import scala.util.Sorting

Sorting.quickSort(yourArray)(new Ordering[Array[String]] {
  def compare(x: Array[String], y: Array[String]) = {
    x(3) compare y(3)
  }
})

My array is Array[Array[String]], x(3) is one field which you want to compare. Of course, if you want to reverse sorting, you just need to use y(3) compare x(3) to replace x(3) compare y(3).

If your array is other type, you just need to use your type to replace Array[String]

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