Databases
StackOverflow2013
Postsdbo
POSort a list by an ordered index
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POSort a list by an ordered index
    primarykey
    data
    text
    <p>Let us assume that I have the following two sequences:</p> <pre><code>val index = Seq(2,5,1,4,7,6,3) val unsorted = Seq(7,6,5,4,3,2,1) </code></pre> <p>The first is the index by which the second should be sorted. My current solution is to traverse over the index and construct a new sequence with the found elements from the unsorted sequence.</p> <pre><code>val sorted = index.foldLeft(Seq[Int]()) { (s, num) =&gt; s ++ Seq(unsorted.find(_ == num).get) } </code></pre> <p>But this solution seems very inefficient and error-prone to me. On every iteration it searches the complete unsorted sequence. And if the index and the unsorted list aren't in sync, then either an error will be thrown or an element will be omitted. In both cases, the not in sync elements should be appended to the ordered sequence.</p> <p>Is there a more efficient and solid solution for this problem? Or is there a sort algorithm which fits into this paradigm?</p> <hr> <p><strong>Note</strong>: This is a constructed example. In reality I would like to sort a list of mongodb documents by an ordered list of document Id's.</p> <hr> <p><strong>Update 1</strong></p> <p>I've selected the answer from Marius Danila because it seems the more fastest and scala-ish solution for my problem. It doesn't come with a not in sync item solution, but this could be easily implemented.</p> <p>So here is the updated solution:</p> <pre><code>def sort[T: ClassTag, Key](index: Seq[Key], unsorted: Seq[T], key: T =&gt; Key): Seq[T] = { val positionMapping = HashMap(index.zipWithIndex: _*) val inSync = new Array[T](unsorted.size) val notInSync = new ArrayBuffer[T]() for (item &lt;- unsorted) { if (positionMapping.contains(key(item))) { inSync(positionMapping(key(item))) = item } else { notInSync.append(item) } } inSync.filterNot(_ == null) ++ notInSync } </code></pre> <hr> <p><strong>Update 2</strong></p> <p>The approach suggested by Bask.cc seems the correct answer. It also doesn't consider the not in sync issue, but this can also be easily implemented.</p> <pre><code>val index: Seq[String] val entities: Seq[Foo] val idToEntityMap = entities.map(e =&gt; e.id -&gt; e).toMap val sorted = index.map(idToEntityMap) val result = sorted ++ entities.filterNot(sorted.toSet) </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USakkie
    1. USakkie
    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. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POSort a list by an ordered index
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POSort a list by an ordered index
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POSort a list by an ordered index
      1. This table or related slice is empty.
      1. VTUpMod
    1. COAlso if you are using the dafault immutable `Seq` you end up building a lot of temporary objects.
      singulars
      1. POSort a list by an ordered index
      1. USmonnef
    2. CO@flavian I use reactivemongo to querying the database. But can I use $orderBy to sort with an external index? I thought I can sort only by a field in ascending or descending order. I could save the order in the documents, but then I must update all documents if a position has changed. With the current solution I create only a new index.
      singulars
      1. POSort a list by an ordered index
      1. USakkie
 

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