Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>As of <a href="https://github.com/scala/scala/commit/73f7001d963a80950751b4e13b95b05d2526edc8">this commit</a> it's a lot easier to "enrich" Scala collections than it was when Rex gave his excellent answer. For simple cases it might look like this,</p> <pre><code>import scala.collection.generic.{ CanBuildFrom, FromRepr, HasElem } import language.implicitConversions class FilterMapImpl[A, Repr](val r : Repr)(implicit hasElem : HasElem[Repr, A]) { def filterMap[B, That](f : A =&gt; Option[B]) (implicit cbf : CanBuildFrom[Repr, B, That]) : That = r.flatMap(f(_).toSeq) } implicit def filterMap[Repr : FromRepr](r : Repr) = new FilterMapImpl(r) </code></pre> <p>which adds a "same result type" respecting <code>filterMap</code> operation to all <code>GenTraversableLike</code>s,</p> <pre><code>scala&gt; val l = List(1, 2, 3, 4, 5) l: List[Int] = List(1, 2, 3, 4, 5) scala&gt; l.filterMap(i =&gt; if(i % 2 == 0) Some(i) else None) res0: List[Int] = List(2, 4) scala&gt; val a = Array(1, 2, 3, 4, 5) a: Array[Int] = Array(1, 2, 3, 4, 5) scala&gt; a.filterMap(i =&gt; if(i % 2 == 0) Some(i) else None) res1: Array[Int] = Array(2, 4) scala&gt; val s = "Hello World" s: String = Hello World scala&gt; s.filterMap(c =&gt; if(c &gt;= 'A' &amp;&amp; c &lt;= 'Z') Some(c) else None) res2: String = HW </code></pre> <p>And for the example from the question, the solution now looks like,</p> <pre><code>class GroupIdenticalImpl[A, Repr : FromRepr](val r: Repr) (implicit hasElem : HasElem[Repr, A]) { def groupIdentical[That](implicit cbf: CanBuildFrom[Repr,Repr,That]): That = { val builder = cbf(r) def group(r: Repr) : Unit = { val first = r.head val (same, rest) = r.span(_ == first) builder += same if(!rest.isEmpty) group(rest) } if(!r.isEmpty) group(r) builder.result } } implicit def groupIdentical[Repr : FromRepr](r: Repr) = new GroupIdenticalImpl(r) </code></pre> <p>Sample REPL session,</p> <pre><code>scala&gt; val l = List(1, 1, 2, 2, 3, 3, 1, 1) l: List[Int] = List(1, 1, 2, 2, 3, 3, 1, 1) scala&gt; l.groupIdentical res0: List[List[Int]] = List(List(1, 1),List(2, 2),List(3, 3),List(1, 1)) scala&gt; val a = Array(1, 1, 2, 2, 3, 3, 1, 1) a: Array[Int] = Array(1, 1, 2, 2, 3, 3, 1, 1) scala&gt; a.groupIdentical res1: Array[Array[Int]] = Array(Array(1, 1),Array(2, 2),Array(3, 3),Array(1, 1)) scala&gt; val s = "11223311" s: String = 11223311 scala&gt; s.groupIdentical res2: scala.collection.immutable.IndexedSeq[String] = Vector(11, 22, 33, 11) </code></pre> <p>Again, note that the same result type principle has been observed in exactly the same way that it would have been had <code>groupIdentical</code> been directly defined on <code>GenTraversableLike</code>.</p>
    singulars
    1. This table or related slice is empty.
    1. POHow do I apply the enrich-my-library pattern to Scala collections?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USMiles Sabin
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COYay! There are _even more_ magical pieces to keep track of this way, but they all combine nicely! It's a relief to not have to worry about each non-collection-hierarchy collection.
      singulars
      1. PO
      1. USRex Kerr
    2. COToo bad Iterator is gratuitously excluded since my one-line change was refused. "error: could not find implicit value for evidence parameter of type scala.collection.generic.FromRepr[Iterator[Int]]"
      singulars
      1. PO
      1. USpsp
    3. COWhich one-line change was refused?
      singulars
      1. PO
      1. USMiles Sabin
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload