With **Swift 3 &amp; 4**, pi is now defined as a static variable on the floating point number types `Double`, `Float` and `CGFloat`, so no specific imports are required any more:

    Double.pi
    Float.pi
    CGFloat.pi

Also note that the actual type of `.pi` can be inferred by the compiler. So, in situations where it&#39;s clear from the context that you are using e.g. `CGFloat`, you can just use `.pi` (thanks to @Qbyte and @rickster for pointing that out in the comments). 

For **older versions of Swift**:

`M_PI` is originally defined in `Darwin` but is also contained in `Foundation` and `UIKit`, so importing any of these will give you the right access.

    import Darwin // or Foundation or UIKit
    
    let pi = M_PI


**Note:**
As noted in the comments, pi can also be used as _unicode_ character in Swift, so you might as well do

    let π = M_PI

`alt + p` is the shortcut (on US-keyboards) that will create the `π` unicode character.


`import Darwin` is not needed all M_x are visible with the `import Foundation` 

( Xcode Version 6.4 (6E35b) )

warning: &#39;M_PI&#39; is deprecated: Please use &#39;Double.pi&#39; or &#39;.pi&#39; to get the value of correct type and avoid casting. 

surprisingly, .pi also works fine. 
M_PI is deprecated as of Swift 4.2.1, Xcode 10.1, which is the current version I am using. SO, Use .pi, or Double.pi 

I have an element with `class=&#39;myTestClass&#39;`. How do I apply a css style to all children of this elements? I only want to apply the style to the elements children. Not its grand children.

I could use

    .myTestClass &gt; div {
      margin: 0 20px;
    }

which work for all `div` children, but I would like a solution which works for all children. I thought I could use `*`, but

    .myTestClass &gt; * {
      margin: 0 20px;
    } 

does not work. 

Edit

The `.myTestClass &gt; *` selector does not apply the rule in firefox 26, and there is no other rule for margin according to firebug. And it works if I replace `*` with `div`. 


How do I apply a style to all children of an element

So I have initialized an empty pandas DataFrame and I would like to iteratively append lists (or Series) as rows in this DataFrame. What is the best way of doing this?




Appending a list or series to a pandas DataFrame as a row?

I am trying to find a way to _include the PI constant in my Swift code_. I already found help in another answer, to `import Darwin` which I know gives me access to _C functions_.

I also checked the `Math` package  in `Darwin` and came across the following declaration:

`var M_PI: Double { get } /* pi             */ `

So, I assume there is a way to use PI in the code, I just don&#39;t know _how_...

How to get mathemical PI constant in Swift

I am trying to find a way to include the PI constant in my Swift code. I already found help in another answer, to <code>import Darwin</code> which I know gives me access to C functions.
I also checked the <code>Math</code> package in <code>Darwin</code> and came across the following declaration:
<code>var M_PI: Double { get } /* pi */ </code>
So, I assume there is a way to use PI in the code, I just don't know how...

Simple question here. I have a UIButton, currencySelector, and I want to programmatically change the text. Here&#39;s what I have:

    currencySelector.text = &quot;foobar&quot;

Xcode gives me the error &quot;Expected Declaration&quot;. What am I doing wrong, and how can I make the button&#39;s text change?

Changing text of UIButton programmatically swift

**Background**

I am trying to encode a String-style enum using the NSCoding protocol, but I am running into errors converting to and back from String.

I get the following errors while decoding and encoding:

*String is not convertible to Stage*

*Extra argument ForKey: in call*


**Code**

        enum Stage : String
        {
            case DisplayAll    = &quot;Display All&quot;
            case HideQuarter   = &quot;Hide Quarter&quot;
            case HideHalf      = &quot;Hide Half&quot;
            case HideTwoThirds = &quot;Hide Two Thirds&quot;
            case HideAll       = &quot;Hide All&quot;
        }
        
        class AppState : NSCoding, NSObject
        {
            var idx   = 0
            var stage = Stage.DisplayAll
        
            override init() {}
        
            required init(coder aDecoder: NSCoder) {
                self.idx   = aDecoder.decodeIntegerForKey( &quot;idx&quot;   )
                self.stage = aDecoder.decodeObjectForKey(  &quot;stage&quot; ) as String    // ERROR
            }
            
            func encodeWithCoder(aCoder: NSCoder) {
                aCoder.encodeInteger( self.idx,             forKey:&quot;idx&quot;   )
                aCoder.encodeObject(  self.stage as String, forKey:&quot;stage&quot; )  // ERROR
            }
    
        // ...
    
        }

How do I encode enum using NSCoder in swift?

I have a project that was started in Objective-C, and I am trying to import some Swift code into the same class files that I have previously written Objective-C in.

I have consulted the Apple [docs][1] on using Swift and Objective-C in the same project, as well as SO [question][2] like this, but still no avail: I continue to get the file not found error after putting in `#import &quot;NewTestApp-Swift.h&quot;` (`NewTestApp` is the name of the Product and module).

Here is what I have done so far:

1. In `Define Modules`, selected `YES` for the app.
2. Ensured that the Product Module name did not have any space in it (see screenshot below question)

I have tried using `#import &quot;NewTestApp-Swift.h&quot;` inside `ViewController.m`, `ViewController.h` and `AppDelegate.m` but none of them has worked. 

What else am I doing incorrectly? Thanks for your help.

----

Screenshot of settings:

![enter image description here][3]

---- 

Errors that I am presently encountering:

![enter image description here][4]


  [1]: https://developer.apple.com/library/ios/documentation/swift/conceptual/buildingcocoaapps/MixandMatch.html
  [2]: https://stackoverflow.com/questions/24062618/swift-to-objective-c-header-not-created-in-xcode-6
  [3]: http://i.stack.imgur.com/OV6UX.png
  [4]: http://i.imgur.com/7UfBZTo.png

Importing Project-Swift.h into a Objective-C class...file not found

I have checked several links on how to convert UIColor codes to HEX however I am not sure on how to  call to the method to display them in NSLog. I haven&#39;t got the reputation to comment so posting as a question is my last resort. **I want it to display when I run my app in the log.**

Second, where do I input the RGB color number ( R = 30, G = 171, B = 13)? I see that all examples use Array [0], [1], [2] which normally refers to index position, so where do I add the color values?

I have this code:

    - (NSString *) hexFromUIColor:(UIColor *)color {
    
        if (CGColorGetNumberOfComponents(color.CGColor) &lt; 4) {
            const CGFloat *components = CGColorGetComponents(color.CGColor);
            color = [UIColor colorWithRed:components[30] green:components[141] blue:components[13] alpha:components[1]];
        }
        if (CGColorSpaceGetModel(CGColorGetColorSpace(color.CGColor)) != kCGColorSpaceModelRGB) {
            return [NSString stringWithFormat:@&quot;#FFFFFF&quot;];
        }
        return [NSString stringWithFormat:@&quot;#%02X%02X%02X&quot;, (int)((CGColorGetComponents(color.CGColor))[0]*255.0), (int)((CGColorGetComponents(color.CGColor))[1]*255.0), (int)((CGColorGetComponents(color.CGColor))[2]*255.0)];

    }


Links I have checked:

https://stackoverflow.com/questions/10285365/hex-color-from-uicolor/13134326#13134326

https://stackoverflow.com/questions/3805177/how-to-convert-hex-rgb-color-codes-to-uicolor

I have tried to call the method in viewDidLoad however it wont work without UIColor. I am sure it&#39;s something simple. 

Thanks to anyone who answers.

What is the code I use in my viewDidLoad to call to this method in order to display in NSLog?

How to convert UIColor to HEX and display in NSLog

I&#39;m not sure what I&#39;m doing wrong here, but when I save the first time into coredata, it works just fine. When I try to overwrite that, it doesn&#39;t.


    func testStuff() {
        var token = loadLoginData()
        println(&quot;Token \(token)&quot;)
        saveLoginData(&quot;New Token&quot;)
        var newToken = loadLoginData()
        println(&quot;Token \(newToken)&quot;)
    }

    func saveLoginData(accessToken: String) {
        var appDel: AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)
        var context: NSManagedObjectContext = appDel.managedObjectContext!
        // save data to core data
        var loginData = NSEntityDescription.insertNewObjectForEntityForName(&quot;LoginData&quot;, inManagedObjectContext: context) as NSManagedObject
        loginData.setValue(accessToken, forKey: &quot;accessToken&quot;)
        context.save(nil)
        println(&quot;Done saving user&quot;)
    }

    /* Output
    Token Optional(&quot;12345&quot;)
    Done saving user
    Token Optional(&quot;12345&quot;)
    */

Load Login Data Func
the function that calls on saveLogin data

    func loadLoginData() -&gt; String? {
        var appDel: AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)
        var context: NSManagedObjectContext = appDel.managedObjectContext!
        
        var request = NSFetchRequest(entityName: &quot;LoginData&quot;)
        request.returnsObjectsAsFaults = false
        
        var results: NSArray = context.executeFetchRequest(request, error: nil)!
        if (results.count &gt; 0) {
            var userData: NSManagedObject = results[0] as NSManagedObject
            var accessToken: String = userData.valueForKey(&quot;accessToken&quot;) as String

            return accessToken.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())
            
        } else {
            println(&quot;0 results returned, potential error&quot;)
            return nil
        }
    }


How do you update a CoreData entry that has already been saved in Swift?

According to this [post](https://stackoverflow.com/questions/11995069/finding-factors-of-a-number-not-getting-accurate-results), we can get all divisors of a number through the following codes.

	for (int i = 1; i &lt;= num; ++i){
		if (num % i == 0)
			cout &lt;&lt; i &lt;&lt; endl;
	}

For example, the divisors of number `24` are `1 2 3 4 6 8 12 24`.

After searching some related posts, I did not find any good solutions. Is there any efficient way to accomplish this?

My solution:

 1. Find all prime factors of the given number through this [solution](http://www.geeksforgeeks.org/print-all-prime-factors-of-a-given-number/).
 2. Get all possible combinations of those prime factors.

However, it doesn&#39;t seem to be a good one.

Efficiently getting all divisors of a given number

I&#39;m working on a problem that has to do with calculating angles of refraction and what not. However, it seems that I&#39;m unable to use the numpy.sin() function in degrees. I have tried to use numpy.degrees() and numpy.rad2deg().

    numpy.sin(90)

    numpy.degrees(numpy.sin(90))

Both return ~ 0.894 and ~ 51.2 respectively.

Thanks for your help.

numpy.sin function in degrees?

I come up with this

    n=1;
    curAvg = 0;
    loop{
      curAvg = curAvg + (newNum - curAvg)/n;
      n++;
    }
I think highlights of this way are:&lt;br&gt;
- It avoids big numbers (and possible overflow if you would sum and then divide)&lt;br&gt;
- you save one register (not need to store sum)

The trouble might be with summing error - but I assume that generally there shall be balanced numbers of round up and round down so the error shall not sum up dramatically.

Do you see any pitfalls in this solution?
Have you any better proposal?

How to efficiently compute average on the fly (moving average)?

I&#39;m currently working on a simple 3D panorama viewer for a website. For mobile performance reasons I&#39;m using the Three.js [CSS&amp;nbsp;3 renderer][1]. This requires a cube map, split up into six single images.

I&#39;m recording the images on the iPhone with Google [Photo Sphere][2], or similar apps that create 2:1 equirectangular panoramas. I then resize and convert these to a cubemap with this website: http://gonchar.me/panorama/ (Flash)

Preferably, I&#39;d like to *do the conversion myself*, either on the fly in Three.js, if that&#39;s possible, or in Photoshop. I found Andrew Hazelden&#39;s Photoshop actions, and they seem kind of close, but no direct conversion is available. Is there a mathematical way to convert these, or some sort of script that does it? I&#39;d like to avoid going through a 3D application like [Blender][3], if possible.

Maybe this is a long shot, but I thought I&#39;d ask. I have okay experience with JavaScript, but I&#39;m pretty new to Three.js. I&#39;m also hesitant to rely on the [WebGL][4] functionality, since it seems either slow or buggy on mobile devices. Support is also still spotty.

  [1]: https://github.com/mrdoob/three.js/blob/master/examples/css3d_panorama.html
  [2]: https://en.wikipedia.org/wiki/Google_Camera#Photo_Sphere
  [3]: https://en.wikipedia.org/wiki/Blender_%28software%29
  [4]: https://en.wikipedia.org/wiki/WebGL






Convert 2:1 equirectangular panorama to cube map

Recently I was going through an [old blog post by Eric Lippert](http://ericlippert.com/2008/05/23/precedence-vs-associativity-vs-order/ &quot;Click here to go to original post&quot;) 
in which, while writing about associativity he mentions that in C#, `(a + b) + c` is not equivalent to `a + (b + c)` for certain values of a, b, c. 

I am not able to figure out for **what types and range of arithmetic values** might that hold true and why.

Content Type	Original Author	Original Content on Stackoverflow
Question	nburk	View Question on Stackoverflow
Solution 1 - Swift	nburk	View Answer on Stackoverflow
Solution 2 - Swift	Guyvo	View Answer on Stackoverflow
Solution 3 - Swift	Sree	View Answer on Stackoverflow

How to get mathemical PI constant in Swift

Swift Problem Overview

Swift Solutions

Solution 1 - Swift

Solution 2 - Swift

Solution 3 - Swift

Appending a list or series to a pandas DataFrame as a row?

How do I apply a style to all children of an element

Attributions