    def foo(msf: String, o: AnyRef, os: AnyRef*) = 
      println( String.format(msf, (o :: os.toList).toArray : _* ))

    def foo(msf: String, o: AnyRef, os: AnyRef*) =
      println( String.format(msf, o :: os.toList : _* ) )

or

    def foo(msf: String, o: AnyRef, os: AnyRef*) =
          println( msf format (o :: os.toList : _* ) )

I much prefer the latter, though it has no locale* support.

* Scala 2.8 does have locale support with RichString&#39;s format.



I have a continuous value for which I&#39;d like to calculate an [exponential moving average](http://en.wikipedia.org/wiki/Exponential_moving_average#Exponential_moving_average). Normally I&#39;d just use the standard formula for this:

* S&lt;sub&gt;n&lt;/sub&gt; = &amp;alpha;Y + (1-&amp;alpha;)S&lt;sub&gt;n-1&lt;/sub&gt;

where S&lt;sub&gt;n&lt;/sub&gt; is the new average, &amp;alpha; is the alpha, Y is the sample, and S&lt;sub&gt;n-1&lt;/sub&gt; is the previous average.

Unfortunately, due to various issues I don&#39;t have a consistent sample time. I may know I can sample at the most, say, once per millisecond, but due to factors out of my control, I may not be able to take a sample for several milliseconds at a time. A likely more common case, however, is that I simple sample a bit early or late: instead of sampling at 0, 1 and 2 ms. I sample at 0, 0.9 and 2.1 ms. I do anticipate that, regardless of delays, my sampling frequency will be far, far above the Nyquist limit, and thus I need not worry about aliasing.

I reckon that I can deal with this in a more-or-less reasonable way by varying the alpha appropriately, based on the length of time since the last sample.

Part of my reasoning that this will work is that the EMA &quot;interpolates linearly&quot; between the previous data point and the current one. If we consider calculating an EMA of the following list of samples at intervals t: [0,1,2,3,4]. We should get the same result if we use interval 2t, where the inputs become [0,2,4], right? If the EMA had assumed that, at t&lt;sub&gt;2&lt;/sub&gt; the value had been 2 since t&lt;sub&gt;0&lt;/sub&gt;, that would be the same as the interval t calculation calculating on [0,2,2,4,4], which it&#39;s not doing. Or does that make sense at all?

Can someone tell me how to vary the alpha appropriately? &quot;Please show your work.&quot; I.e., show me the math that proves that your method really is doing the right thing.

Exponential Moving Average Sampled at Varying Times

I have what I thought was a simple scenario - using TortoiseSVN:

1) I made a branch (B2) of an application (to work on implementing image sprites &amp; JAWR).

2) Testing &amp; development went on as normal on the trunk.

3) I re-based the branch a couple of times over the last few days by:

3.1) Merged trunk (by range of revisions) to my branch-b2 working copy, resolving conflicts during the merge.

3.2) (after testing branch-b2), I commit the re-based branch-b2.

This all worked as I expected.  But merging the branch back into the trunk is having its way with me:

4) After all updates committed in branch-b2; I make sure I do an SVN Update on trunk and branch-b2.

5) Then, I try to merge (range of revisions) from branch-b2 into the trunk.  However, for any new file that had been added to the trunk, and subsequently added to branch-b2 when I rebased it, I get a tree-conflict.  I&#39;m not sure what the proper way is to resolve these conflicts.


The most typical advice I&#39;ve seen is to either delete the tree-conflict files from the trunk, then merge the branch over; or delete the entire trunk, copy the branch files over, and then commit them as a new version in the trunk.  Neither of those options seems like a good idea- first one is a pain, and both seem like they would lose file revision histories.

What&#39;d I do wrong, and how do I fix it?

SVN - unable to merge branch back into trunk - numerous tree-conflicts

I&#39;m tearing my hair out trying to figure out how to do the following:

    def foo(msf: String, o: Any, os: Any*) = {
        println( String.format(msf, o :: List(os:_*)) )
    }

There&#39;s a reason why I have to declare the method with an `o` and an `os` `Seq` separately. Basically, I end up with the format method called with a single object parameter (of type `List `). Attempting:

    def foo(msf: String, o: Any, os: Any*) = {
        println( String.format(msf, (o :: List(os:_*))).toArray )
    }

Gives me the type error:
 &gt; found: Array[Any]
 &gt;
 &gt; required Seq[java.lang.Object]

I&#39;ve tried casting, which compiles but fails for pretty much the same reason as the first example. When I try

    println(String.format(msg, (o :: List(os:_*)) :_* ))

this fails to compile with implicit conversion ambiguity (`any2ArrowAssoc` and `any2stringadd`)


Using varargs from Scala

I'm tearing my hair out trying to figure out how to do the following:
<pre><code class="hljs language-less">def foo(msf: String, o: Any, os: Any*) = {
 println( String.format(msf, o :: List(os:_*)) )
}
</code></pre>
There's a reason why I have to declare the method with an <code>o</code> and an <code>os</code> <code>Seq</code> separately. Basically, I end up with the format method called with a single object parameter (of type <code>List </code>). Attempting:
<pre><code class="hljs language-less">def foo(msf: String, o: Any, os: Any*) = {
 println( String.format(msf, (o :: List(os:_*))).toArray )
}
</code></pre>
Gives me the type error:
> found: Array[Any]
>
> required Seq[java.lang.Object]
I've tried casting, which compiles but fails for pretty much the same reason as the first example. When I try
<pre><code class="hljs language-less">println(String.format(msg, (o :: List(os:_*)) :_* ))
</code></pre>
this fails to compile with implicit conversion ambiguity (<code>any2ArrowAssoc</code> and <code>any2stringadd</code>)

What are the hidden features of Scala that every Scala developer should be aware of?

One hidden feature per answer, please.


Hidden features of Scala

I understand Ruby and Python&#39;s yield. What does Scala&#39;s yield do?


What is Scala&#39;s yield?

Are there any libraries written for Scala enabling Functional Reactive Programming?

Functional Reactive Programming in Scala

What is the difference between the `map` and `flatMap` functions of `Iterable`?

scala Iterable#map vs. Iterable#flatMap

Is there an easy way to convert a    

    java.lang.Iterable[_]

 to a

    Scala.Iterable[_]
 ? 


How can I convert a Java Iterable to a Scala Iterable?

I have a class that holds an &quot;error&quot; function that will format some text.  I want to accept a variable number of arguments and then format them using printf.

**Example:**

    class MyClass
    {
    public:
        void Error(const char* format, ...);
    };

The Error method should take in the parameters, call printf/sprintf to format it and then do something with it.  I don&#39;t want to write all the formatting myself so it makes sense to try and figure out how to use the existing formatting.

How to pass variable number of arguments to printf/sprintf

I have a PHP function that takes a variable number of arguments (using `func_num_args()` and `func_get_args()`), but the number of arguments I want to pass the function depends on the length of an array. Is there a way to _call_ a PHP function with a variable number of arguments?

How to pass variable number of arguments to a PHP function

I have a float[] and i would like to get a list with the same elements. I could do the ugly thing of adding them one by one but i wanted to use the Arrays.asList method. There is a problem though. This works:

    List&lt;Integer&gt; list = Arrays.asList(1,2,3,4,5);

But this does not.

    int[] ints = new int[] {1,2,3,4,5};
    List&lt;Integer&gt; list = Arrays.asList(ints);

The asList method accepts a varargs parameter which to the extends of my knowledge is a &quot;shorthand&quot; for an array. 

Questions:  

  - Why does the second piece of code returns a `List&lt;int[]&gt;` but not `List&lt;int&gt;`.

  - Is there a way to correct it?

  - Why doesn&#39;t autoboxing work here; i.e. `int[]` to `Integer[]`?

Arrays.asList() not working as it should?

How can I write a function that accepts a variable number of arguments? Is this possible, how?



Variable number of arguments in C++?

Is it possible to send a variable number of arguments to a JavaScript function, from an array? 

    var arr = [&#39;a&#39;,&#39;b&#39;,&#39;c&#39;]

    var func = function()
    {
        // debug 
        alert(arguments.length);
        //
        for(arg in arguments)
            alert(arg);
    }

    func(&#39;a&#39;,&#39;b&#39;,&#39;c&#39;,&#39;d&#39;); // prints 4 which is what I want, then &#39;a&#39;,&#39;b&#39;,&#39;c&#39;,&#39;d&#39;
    func(arr); // prints 1, then &#39;Array&#39;


I&#39;ve recently written a lot of Python and it&#39;s a wonderful pattern to be able to accept varargs and send them. e.g.

    def func(*args):
       print len(args)
       for i in args:
           print i

    func(&#39;a&#39;,&#39;b&#39;,&#39;c&#39;,&#39;d&#39;); // prints 4 which is what I want, then &#39;a&#39;,&#39;b&#39;,&#39;c&#39;,&#39;d&#39;
    func(*arr) // prints 4 which is what I want, then &#39;a&#39;,&#39;b&#39;,&#39;c&#39;,&#39;d&#39;


Is it possible in JavaScript to send an array to be treated __as__ the arguments array? 





Content Type	Original Author	Original Content on Stackoverflow
Question	oxbow_lakes	View Question on Stackoverflow
Solution 1 - Scala	James Iry	View Answer on Stackoverflow
Solution 2 - Scala	Daniel C. Sobral	View Answer on Stackoverflow

Using varargs from Scala

Scala Problem Overview

Scala Solutions

Solution 1 - Scala

Solution 2 - Scala

SVN - unable to merge branch back into trunk - numerous tree-conflicts

Exponential Moving Average Sampled at Varying Times

Attributions