Wednesday, November 21, 2012

Configure Sublime Text 2 (ST2) JSHint plugin

brew install node
brew install npm
npm install jshint -g

Install ST2 Package Control:

Restart ST2
CMD-Shift-P opens Package Control dialog (OSX)
Type:  Install  and hit enter  << That will select Package Control:  Install Package
Type:  sublime-jshint and hit enter

Now, when you edit a javascript file and save it, you will get the following error message:

Error trying to parse build system: No data in ~/Library/Application Support/Sublime Text 2/Packages/JSHint/JSHint.sublime-build:1:1

cd /Volumes/HoneyBadger1TB/Users/lex/Library/Application\ Support/Sublime\ Text\ 2/Packages
ln -s Sublime-JSHint JSHint

Now, when you save files in ST2 JSHint will display messages at the bottom of your editor window..

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Thursday, November 15, 2012

Calculating totals from sub lists using Scala


Given a list of users' names and permissionIds
I want a total count of each permissionId
So that I can see which permissions are required most frequently

Given the following data about two users (Alice and Bob)...


I want to map those users' permsission Ids (1, 2, 3) to each one's count.

permissionId  total
1                    1
2                    2
3                    1


Here's how to accomplish this in Scala:

scala> case class User(name: String, permissionIds: List[Int])
defined class User

scala> val user1 = User("Alice", List(1, 2))
user1: User = User(Alice,List(1, 2))

scala> val user2 = User("Bob", List(2, 3))
user2: User = User(Bob,List(2, 3))

scala> val users = List(user1, user2)
users: List[User] = List(User(Alice,List(1, 2)), User(Bob,List(2, 3)))

scala> val permissionIdTotals =
permissionIdTotals: scala.collection.immutable.Map[Int,Int] = Map(3 -> 1, 1 -> 1, 2 -> 2)

Here's how the permissionIdTotal calculation is broken down:

res0: List[List[Int]] = List(List(1, 2), List(2, 3))

res1: List[Int] = List(1, 2, 2, 3)

res2: scala.collection.immutable.Map[Int,List[Int]] = Map(3 -> List(3), 1 -> List(1), 2 -> List(2, 2))

res3: scala.collection.immutable.Map[Int,Int] = Map(3 -> 1, 1 -> 1, 2 -> 2)


Note that I did not use variables to store temporary values;  It uses a series of chained function calls to arrive at the final calculation.

Given a set of input values, the results will always be the same.  There are not side effects.

The converse of functional programming is imperative programming.

Imperative programming tends to be easier to understand, but requires more lines of code and may not be safe to use when attempting to satisfy concurrent programming requirements.

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