I found out how to invert a matrix on SO, but I didn’t understand the solution, so I thought I’d talk more about it here. First of all, there isn’t a one-off inverse function in the Accelerate framework. You need to calculate the LU facotrization first using dgetrf_(), and then plug that data into dgetri_() to calculate the inverse.
Continue reading Matrix Inversion Using Swift and Accelerate
In this post I’ll walk through setting up a hierarchical view with expanding nodes using NSOutlineView and NSTreeController. This is the sort of thing you’d want if you had to describe a file system. In this example I’ll be using Xcode 7 and Swift 2.
Continue reading Using NSOutlineView and NSTreeController to Create a Tree
I found this so helpful on StackOverflow, I thought I’d re-post it here for my personal reference. The snippet below is used to take a 1024-by-1024 pixel PNG file named Icon1024.png, and create smaller resolution copies in an iconset directory, which can be used later when you deploy your app.
mkdir MyIcon.iconset sips -z 16 16 Icon1024.png --out MyIcon.iconset/icon_16x16.png sips -z 32 32 Icon1024.png --out MyIcon.iconset/icon_16x16@2x.png sips -z 32 32 Icon1024.png --out MyIcon.iconset/icon_32x32.png sips -z 64 64 Icon1024.png --out MyIcon.iconset/icon_32x32@2x.png sips -z 128 128 Icon1024.png --out MyIcon.iconset/icon_128x128.png sips -z 256 256 Icon1024.png --out MyIcon.iconset/icon_128x128@2x.png sips -z 256 256 Icon1024.png --out MyIcon.iconset/icon_256x256.png sips -z 512 512 Icon1024.png --out MyIcon.iconset/icon_256x256@2x.png sips -z 512 512 Icon1024.png --out MyIcon.iconset/icon_512x512.png cp Icon1024.png MyIcon.iconset/icon_512x512@2x.png iconutil -c icns MyIcon.iconset rm -R MyIcon.iconset
The next to last line uses the iconutil utility to convert an iconset into an icns file, but it can also work the other way. (See man iconutil for more information.)
I thought that .pex files were the way to go for distributing Python applications to OS X users, but it was only partially successful. For one, users needed to reinstall Python with Homebrew, which isn’t difficult, it’s just awkward explaining to people that the Python distribution that ships with Mac isn’t the same Python distribution that exists in the wild. Their next question is invariably, “how will this affect the rest of my system?” I can’t answer that. I can’t guarantee that things will be future-proof.
And then I found app2py (or five dollars) which creates a Mac application bundle out of a Python script. It worked like a charm. The best thing is that you don’t have to write a stupid setup.py file, it writes one for you. That’s five minutes of your precious time you can look at cat videos with, or whatever.
You can install this using pip, so that’s cool. Next, you do as the tutorial explains,
py2applet --make-setup MyApplication.py
This will create a setup.py file. Finally, for deployment, you build the distribution with a non-Mac Python installation. (If you haven’t already run brew install python you’ll want to run that.) My brew installation of the Python landed somewhere in /usr/local/Cellar/....
/usr/local/Cellar/python/2.7.8_2/bin/python setup.py py2app
This will create a standalone Python application that you can distribute painlessly to your Mac colleagues.
I saw this on Hacker News the other day, and I didn’t want to lose it somewhere in my Pinboard.in account, so I’ll post it here: Amazon Web Services in Plain English. Enjoy!
I needed to sample lines from a file, and I found this SO post on on the Reservoir Algorithm. The code below lets you sample a single line from a file in O(n) time. What makes this code special, besides it’s linear time, simplicity and elegance, is the fact that the file you’re sampling from doesn’t need to fit in memory.
import random
def random_line( filename ):
hdl = open( filename, "r" )
line = next( hdl )
for num, aline in enumerate( hdl ):
if random.randrange(num + 2):
continue
line = aline
return line
Swift2 came out yesterday! For free! I thought that Swift2 would have built-in support for I/O, but it looks like you need to import Cocoa first.
import Cocoa
let data = NSString( string:"Hallo, Welt!" )
let destPath = "/Users/connorjohnson/myFile.txt"
var filemgr = NSFileManager.defaultManager()
do {
try data.writeToFile(destPath, atomically: true, encoding: NSUTF8StringEncoding)
} catch let error as NSError {
print("Error: \(error)")
}
In this post I’ll discuss replacing characters in a string, splitting a string using some value, and using regexes to count the number of matches in a string, and locating the first match in a string. I’m using XCode 6.4 with Swift 1.2. If you’re not sure which version of Swift you’re running, you can call the following from the command line,
$ xcrun swift --version Apple Swift version 1.2 (swiftlang-602.0.53.1 clang-602.0.53) Target: x86_64-apple-darwin15.0.0
I just found this neat Python module called TinyDB. It’s a document based database that is written in pure Python with ~1800(!) lines of code, 40% of which I hear is comments(!!). And there’s full(!!!) test coverage? Which implies that they performed any kind of testing at all? Crazy stuff. In this post I’ll provide a small sample of inserting recipes and querying them.