From [Programming Scala][1]:

    Array(1,2,4,5).sameElements(Array(1,2,4,5))

  [1]: http://www.amazon.com/Programming-Scala-Scalability-Functional-Objects/dp/0596155956

You need to change your last line to

    a.deep == b.deep

to do a deep comparison of the arrays.

      a.corresponds(b){_ == _}

&gt; Scaladoc: `true` if both sequences have
&gt; the same length and `p(x, y)` is `true`
&gt; for all corresponding elements `x` of
&gt; `this` wrapped array and `y` of `that`,
&gt; otherwise `false`

For best performance you should use:

    java.util.Arrays.equals(a, b)

This is very fast and does not require extra object allocation. `Array[T]` in scala is the same as `Object[]` in java. Same story for primitive values like `Int` which is java `int`.

As of Scala 2.13, the `deep` equality approach doesn&#39;t work and errors out:

```scala
val a: Array[Int] = Array(1,2,4,5)
val b: Array[Int] = Array(1,2,4,5)
a.deep == b.deep // error: value deep is not a member of Array[Int]
```

`sameElements` still works in Scala 2.13:

```
a sameElements b // true
```

It didn&#39;t look like most of the provided examples work with multidimensional arrays. For example

   

     val expected = Array(Array(3,-1,0,1),Array(2,2,1,-1),Array(1,-1,2,-1),Array(0,-1,3,4))
     val other = Array(Array(3,-1,0,1),Array(2,2,1,-1),Array(1,-1,2,-1),Array(0,-1,3,4))
    
        assert(other.sameElements(expected))

 returns false, throws an assertion failure

    deep doesn&#39;t seem to be a function defined on Array.


For convenience I imported scalatest matchers and it worked.
    
    import org.scalatest.matchers.should.Matchers._
    other should equal(expected)  







With CSS 3, are there any way to vertically align an block element? Do you have an example?
Thank you.

Align vertically using CSS 3

I am trying port my iPad project to latest iPad 2. I installed iOS 4.3 SDK with Xcode 4.0. When i try to build my project, i&#39;m getting the following error. I don&#39;t know why am i getting this error. Could someone help me to resolve this build error?

&gt; While reading /Users/username/Desktop/iPAD/MyProject/trunk/Resourses/images/top_bar.png pngcrush caught libpng error:
   Not a PNG file..

Could not find file: /Users/username/Library/Developer/Xcode/DerivedData/Project-fmhveawksgdtnraclfizuhrekmzi/Build/Products/Debug-iphoneos/MyApp-Upgraded.app/top_bar.png



iPad: PNG Crush error

    val a: Array[Int] = Array(1,2,4,5)
    val b: Array[Int] = Array(1,2,4,5)
    a==b // false

Is there a pattern-matching way to see if two arrays (or sequences) are equivalent?

How do I compare two arrays in scala?

<pre><code class="hljs language-less">val a: Array[Int] = Array(1,2,4,5)
val b: Array[Int] = Array(1,2,4,5)
a==b // false
</code></pre>
Is there a pattern-matching way to see if two arrays (or sequences) are equivalent?

A fairly simple question. What&#39;s the difference between:

    $merged = array_merge($array1, $array2);

and

    $merged = $array1 + $array2;

?

What&#39;s the difference between array_merge and array + array?

How can I turn a **string** below into an **array**?

    pg_id=2&amp;parent_id=2&amp;document&amp;video 

This is the array I am looking for,

    array(
        &#39;pg_id&#39; =&gt; 2,
        &#39;parent_id&#39; =&gt; 2,
        &#39;document&#39; =&gt; ,
        &#39;video&#39; =&gt;
    )

Parse query string into an array

I have an array of objects.

Is it possible to make a new array that is a copy of this array, but in reverse order?
I was looking for something like this. 

    // my array
    ArrayList&lt;Element&gt; mElements = new ArrayList&lt;Element&gt;();
    // new array
    ArrayList&lt;Element&gt; tempElements = mElements;
    
    tempElements.reverse(); // something to reverse the order of the array



android - reverse the order of an array

I am trying to create a class to handle arrays but I can&#39;t seem to get `array_map()` to work in it.

    &lt;?php
    //Create the test array
    $array = array(1,2,3,4,5,6,7,8,9,10);
    //create the test class
    class test {
	//variable to save array inside class
	public $classarray;
	
	//function to call array_map function with the given array
	public function adding($data) {
		$this-&gt;classarray = array_map($this-&gt;dash(), $data);
	}
	
	// dash function to add a - to both sides of the number of the input array
	public function dash($item) {
		$item2 = &#39;-&#39; . $item . &#39;-&#39;;
		return $item2;
	}
	
    }
    // dumps start array
    var_dump($array);
    //adds line
    echo &#39;&lt;br /&gt;&#39;;
    //creates class object
    $test = new test();
    //classes function adding
    $test-&gt;adding($array);
    // should output the array with values -1-,-2-,-3-,-4-... 
    var_dump($test-&gt;classarray);

**This outputs** 

`array(10) { [0]=&gt; int(1) [1]=&gt; int(2) [2]=&gt; int(3) [3]=&gt; int(4) [4]=&gt; int(5) [5]=&gt; int(6) [6]=&gt; int(7) [7]=&gt; int(8) [8]=&gt; int(9) [9]=&gt; int(10) }`

`Warning: Missing argument 1 for test::dash(), called in D:\xampp\htdocs\trainingdvd\arraytesting.php on line 11 and defined in D:\xampp\htdocs\trainingdvd\arraytesting.php on line 15`

`Warning: array_map() expects parameter 1 to be a valid callback, function &#39;--&#39; not found or invalid function name in D:\xampp\htdocs\trainingdvd\arraytesting.php on line 11 NULL`

What am I doing wrong or does this function just not work inside classes?


array_map not working in classes

After searching for an answer in other posts, I felt I have to ask this.
I looked at &lt;https://stackoverflow.com/questions/237104/javascript-array-containsobj&gt;
and &lt;https://stackoverflow.com/questions/143847/best-way-to-find-an-item-in-a-javascript-array&gt; and couldn&#39;t get the code there to work.

I am capturing an html embed code into an array, so each item is a line of html code.

for example:  

    i[0]=&#39;&lt;param name=\&quot;bgcolor\&quot; value=\&quot;#FFFFFF\&quot; /&gt;&#39;
    i[1]=&#39;&lt;param name=\&quot;width&quot; value=\&quot;640\&quot; /&gt;&#39;
    i[2]=&#39;&lt;param name=\&quot;height\&quot; value=\&quot;360\&quot; /&gt;&#39;   
    i[3]=&#39;more html code&#39; 

I want to search this array and find the line where the word &#39;height&#39; is.

So ideally, I&#39;d like to write a function that returns the index of the item where &#39;height&#39; appears.

Fortunately, there are no duplicates in this array, so there&#39;s only one occurrence.

with simple object search I get &#39;false&#39; returns.

Any idea?






How to search for a string inside an array of strings

As I understand from [this blog post][1]  &quot;type classes&quot; in Scala is just a &quot;pattern&quot; implemented with traits and implicit adapters.

As the blog says if I have trait `A` and an adapter `B -&gt; A` then I can invoke a function, which requires argument of type `A`, with an argument of type `B` without invoking this adapter explicitly.

I found it nice but not particularly useful. Could you give a use case/example, which shows what this feature is useful for ? 


  [1]: http://debasishg.blogspot.com/2010/06/scala-implicits-type-classes-here-i.html

What are type classes in Scala useful for?

One of the most powerful patterns available in Scala is the enrich-my-library* pattern, which uses implicit conversions to _appear_ to add methods to existing classes without requiring dynamic method resolution.  For example, if we wished that all strings had the method `spaces` that counted how many whitespace characters they had, we could:

    class SpaceCounter(s: String) {
      def spaces = s.count(_.isWhitespace)
    }
    implicit def string_counts_spaces(s: String) = new SpaceCounter(s)

    scala&gt; &quot;How many spaces do I have?&quot;.spaces
    res1: Int = 5

Unfortunately, this pattern runs into trouble when dealing with generic collections.  For example, a number of questions have been asked about [grouping items sequentially with collections][1].  There is nothing built in that works in one shot, so this seems an ideal candidate for the enrich-my-library pattern using a generic collection `C` and a generic element type `A`:

    class SequentiallyGroupingCollection[A, C[A] &lt;: Seq[A]](ca: C[A]) {
      def groupIdentical: C[C[A]] = {
        if (ca.isEmpty) C.empty[C[A]]
        else {
          val first = ca.head
          val (same,rest) = ca.span(_ == first)
          same +: (new SequentiallyGroupingCollection(rest)).groupIdentical
        }
      }
    }

except, of course, it _doesn&#39;t work_.  The REPL tells us:

    &lt;console&gt;:12: error: not found: value C
                   if (ca.isEmpty) C.empty[C[A]]
                                   ^
    &lt;console&gt;:16: error: type mismatch;
     found   : Seq[Seq[A]]
     required: C[C[A]]
                     same +: (new SequentiallyGroupingCollection(rest)).groupIdentical
                          ^

There are two problems: how do we get a `C[C[A]]` from an empty `C[A]` list (or from thin air)?  And how do we get a `C[C[A]]` back from the `same +:` line instead of a `Seq[Seq[A]]`?

*&lt;sup&gt; Formerly known as pimp-my-library.&lt;/sup&gt;


  [1]: https://stackoverflow.com/questions/4761386/scala-list-function-for-grouping-consecutive-identical-elements


How do I apply the enrich-my-library pattern to Scala collections?

When creating a `Map` in scala, I call `Map(entities.map{e =&gt; e.id -&gt; e})`, and I get:

    found   : scala.collection.mutable.IndexedSeq[(Int, Entity)]
    required: (Int, Entity)

This is because the signature for `Map.apply` is: `def apply[A, B](elems: (A, B)*): CC[A, B]`,
which requires a varargs style argument.

Is there a way to convert the `IndexedSeq` so that it can be accepted via `Map.apply`?


scala: How to pass an expanded list as varargs into a method?

An _implicit_ question to newcomers to Scala seems to be: where does the compiler look for implicits? I mean implicit because the question never seems to get fully formed, as if there weren&#39;t words for it. :-) For example, where do the values for `integral` below come from?

    scala&gt; import scala.math._
    import scala.math._
    
    scala&gt; def foo[T](t: T)(implicit integral: Integral[T]) {println(integral)}
    foo: [T](t: T)(implicit integral: scala.math.Integral[T])Unit
    
    scala&gt; foo(0)
    scala.math.Numeric$IntIsIntegral$@3dbea611
    
    scala&gt; foo(0L)
    scala.math.Numeric$LongIsIntegral$@48c610af

Another question that does follow up to those who decide to learn the answer to the first question is how does the compiler choose which implicit to use, in certain situations of apparent ambiguity (but that compile anyway)?

For instance, `scala.Predef` defines two conversions from `String`: one to `WrappedString` and another to `StringOps`. Both classes, however, share a lot of methods, so why doesn&#39;t Scala complain about ambiguity when, say, calling `map`?

**Note:** this question was inspired by [this other question][1], in the hopes of stating the problem in a more general manner. The example was copied from there, because it is referred to in the answer.


  [1]: https://stackoverflow.com/questions/5512397/passing-scala-math-integral-as-implicit-parameter

Where does Scala look for implicits?

I have a List, which may contain elements that will compare as equal. I would like a similar List, but with one element removed. So from (A, B, C, B, D) I would like to be able to &quot;remove&quot; just one B to get e.g. (A, C, B, D). The order of the elements in the result does not matter.

I have working code, written in a Lisp-inspired way in Scala. Is there a more idiomatic way
to do this?

The context is a card game where two decks of standard cards are in play, so there may
be duplicate cards but still played one at a time.

    def removeOne(c: Card, left: List[Card], right: List[Card]): List[Card] = {
      if (Nil == right) {
        return left
      }
      if (c == right.head) {
        return left ::: right.tail
      }
      return removeOne(c, right.head :: left, right.tail)
    }
  
    def removeCard(c: Card, cards: List[Card]): List[Card] = {
      return removeOne(c, Nil, cards)
    }


What is an idiomatic Scala way to &quot;remove&quot; one element from an immutable List?

So here&#39;s the situation.  I want to define a case class like so:

    case class A(val s: String)

and I want to define an object to ensure that when I create instances of the class, the value for &#39;s&#39; is always uppercase, like so:

    object A {
      def apply(s: String) = new A(s.toUpperCase)
    }

However, this doesn&#39;t work since Scala is complaining that the apply(s: String) method is defined twice.  I understand that the case class syntax will automatically define it for me, but isn&#39;t there another way I can achieve this?  I&#39;d like to stick with the case class since I want to use it for pattern matching.



How to override apply in a case class companion

I have the following piece of code from [this question](https://stackoverflow.com/questions/2199040/scala-xml-building-adding-children-to-existing-nodes):

    def addChild(n: Node, newChild: Node) = n match {
      case Elem(prefix, label, attribs, scope, child @ _*) =&gt; Elem(prefix, label, attribs, scope, child ++ newChild : _*)
      case _ =&gt; error(&quot;Can only add children to elements!&quot;)
    }

Everything in it is pretty clear, except this piece: `child ++ newChild : _*`


What does it do? 

I understand there is `Seq[Node]` concatenated with another `Node`, and then? What does `: _*` do?



What does `:_*` (colon underscore star) do in Scala?

How to catch multiple exceptions at once in Scala? Is there a better way than in C#: https://stackoverflow.com/questions/136035/catch-multiple-exceptions-at-once

Catching multiple exceptions at once in Scala

I have the following code which recursively operates on each element within a List

    def doMatch(list: List[Int]): Unit = list match {
      case last :: Nil  =&gt; println(&quot;Final element.&quot;)
      case head :: tail =&gt; println(&quot;Recursing...&quot;); doMatch(tail)
    }

Now, ignoring that this functionality is available through _filter()_ and _foreach()_, this works just fine. However, if I try to change it to accept any _Seq[Int]_, I run into problems:

&lt;ul&gt;
&lt;li&gt; Seq doesn&#39;t have ::, but it does have +:, which as I understand is basically the same thing. If I try to match on head +: tail however, the compiler complains &#39;error: not found: value +:&#39;&lt;/li&gt;
&lt;li&gt; Nil is specific to List, and I&#39;m not sure what to replace it with. I&#39;m going to try Seq() if I ever get past the previous problem&lt;/li&gt;
&lt;/ul&gt;

Here is how I think the code should look, except it doesn&#39;t work:

    def doMatch(seq: Seq[Int]): Unit = seq match {
      case last +: Seq() =&gt; println(&quot;Final element.&quot;)
      case head +: tail  =&gt; println(&quot;Recursing...&quot;); doMatch(tail)
    }

Edit: So many good answers! I&#39;m accepting agilesteel&#39;s answer as his was the first that noted that :: isn&#39;t an operator in my example, but a case class and hence the difference.



Scala pattern matching on sequences other than Lists

Take the following function:


    def fMatch(s: String) = {
        s match {
            case &quot;a&quot; =&gt; println(&quot;It was a&quot;)
            case _ =&gt; println(&quot;It was something else&quot;)
        }
    }

This pattern matches nicely:

    scala&gt; fMatch(&quot;a&quot;)
    It was a

    scala&gt; fMatch(&quot;b&quot;)
    It was something else

What I would like to be able to do is the following:

    def mMatch(s: String) = {
        val target: String = &quot;a&quot;
        s match {
            case target =&gt; println(&quot;It was&quot; + target)
            case _ =&gt; println(&quot;It was something else&quot;)
            }
    }

This gives off the following error: 

    fMatch: (s: String)Unit
    &lt;console&gt;:12: error: unreachable code
                   case _ =&gt; println(&quot;It was something else&quot;)

I guess this is because it thinks that target is actually a name you&#39;d like to assign to whatever the input is. Two questions:

1. Why this behaviour? Can&#39;t case just look for existing variables in scope that have appropriate type and use those first and, if none are found, then treat target as a name to patternmatch over?

2. Is there a workaround for this? Any way to pattern match against variables? Ultimately one could use a big if statement, but match case is more elegant.

Content Type	Original Author	Original Content on Stackoverflow
Question	Phil H	View Question on Stackoverflow
Solution 1 - Arrays	sc_ray	View Answer on Stackoverflow
Solution 2 - Arrays	Moritz	View Answer on Stackoverflow
Solution 3 - Arrays	The Archetypal Paul	View Answer on Stackoverflow
Solution 4 - Arrays	jjuraszek	View Answer on Stackoverflow
Solution 5 - Arrays	Powers	View Answer on Stackoverflow
Solution 6 - Arrays	discord	View Answer on Stackoverflow

How do I compare two arrays in scala?

Arrays Problem Overview

Arrays Solutions

Solution 1 - Arrays

Solution 2 - Arrays

Solution 3 - Arrays

Solution 4 - Arrays

Solution 5 - Arrays

Solution 6 - Arrays

iPad: PNG Crush error

Align vertically using CSS 3

Attributions