Scala FAQ: How do I find the unique items in a List, Array, Vector, or other Scala sequence?
Solution: Use the distinct method.
Here's a simple example using a List of integers:
scala> val x = List(1,1,1,2,2,3,3) x: List[Int] = List(1, 1, 1, 2, 2, 3, 3) scala> x.distinct res0: List[Int] = List(1, 2, 3)
As you can see, res0 now contains only the unique elements in the list.
Scala Set FAQ: How do I create a mutable Set in Scala?
To create a mutable set in Scala, first determine the type of set you want. You do this because the mutable Set is actually a trait, and you need to determine which concrete implementation you want.
For instance, if you want a SortedSet of String, define it like this:
val names = scala.collection.mutable.SortedSet[String]()
Then you can add elements to the set later like this:
Normally I just write about solutions, but I thought I'd take a moment today to write about something else. In this case I just wanted to note that it's possible to create an immutable List of mutable data in Scala. This scenario made me wonder, "What does 'immutable' mean?" Let's take a look.
As a first example, we'll create a Person class that has two fields, and the first field (firstName) can change:
I just ran across this scala-lang.org post about using tuples in an anonymous function, and thought it was good enough to reproduce here, with only the solution part.
In essence, the question is, if I have a Map like this, which is really composed of tuples:
Here's a short example of how to use the Scala XML NodeBuffer class:
When you write Scala code like this:
val x = List.range(1, 10) val evens = x.filter((i: Int) => i % 2 == 0)
the following portion of the code is a function literal (also known as an anonymous function):
(i: Int) => i % 2 == 0
When reading this code, it helps to think of this symbol:
The Scala Cookbook is coming soon ... August 21, 2013, to be exact. It’s available for pre-order on Amazon.com now, so I thought I’d share some information about the book here today.
After hearing about ShadajL’s presentation at Scala Days 2013 using a MindWave headset, I decided to buy a headset to see how if it really works. After a little while I got the hang of using the headset, so I decided to try ShadajL’s NeuroSky Scala library (named neuro-thinkgear) to see how it works as well.
If you’re just getting started with Scala and/or the Simple Build Tool, I hope the following video will help. It’s a five-minute introduction to the Simple Build Tool, or SBT:
I hope that was helpful. I'll try to make more Scala and SBT videos as time allows.
If you want to connect to the NeuroSky ThinkGear API -- what they call the ThinkGear Socket Protocol -- this code shows you how to do it, at least in Scala. It consists of a few pieces of code I pulled from this GitHub repo. I wrote this code to help debug a problem I was seeing with the data.
The RawReader class does all the work. It opens a socket on the right port, then sends the necessary JSON to that socket to get things started. After that I just read the raw data that the API writes to the socket.
A few days ago I wrote that I didn’t like the tone of Rod Johnson’s Scala Days keynote address; I thought it was a downer, when it could have been much more uplifting and inspirational, while still getting across some very important points.
Scala String problem: You need to find the difference between two strings, the common characters between two strings, or the unique characters in a string.
You can perform all of these operations with built-in methods. Use the diff method to find the differences between two strings:
To create an order by query using the find method of the MongoDB Casbah driver (Scala), use the sort method, as shown in this example:
Don’t tell anyone (wink wink), but the folks at O’Reilly sent me a box of mini Moo cards with a discount code for the Scala Cookbook. So, me being me, I thought I’d share that code out here so you can save $$$. Here’s the front of the Moo card:
As a quick little bit of code sharing, I gave my Sarah stocks plugin the ability to allow multiple spoken phrases for one command. For instance, a user can now say “check stock prices”, “get stock prices”, or “get stocks” to check their stocks. To do this, I added an array of phrases to the JSON file that describes the Stocks plugin.
Getting to the point of this post, the following Scala source code shows how to read an array of JSON string values using Lift-JSON:
I was just reading Treating Code as an Essay in the book Beautiful Code, and saw this paragraph:
After that, I saw two versions of the famous, “Hello, world” program, one written in Java:
public class Hello {
public static void main(String[] args) {
System.out.println("Hello, world");
}
}
and a second program written in Ruby:
Just a quick note here today that if you want to create a Twitter client in Scala, the Java Twitter4J library looks like a good path to take.
I've shown an example below, where you can see that besides the eight lines of code it takes to create a Scala twitter object, the actual code you need to get information from the Twitter developer API is pretty short.
There currently isn't much in the way of good Scala Lift Framework documentation, particularly for creating web forms, but I thought I'd share whatever good links I can find.
Currently there are only two good links about creating Lift forms, and both of those are on the official liftweb.net website:
I just got the following error message when trying to use the current Yahoo OAuth authentication system to connect to Yahoo Mail: