Learning Methodology

When I learn new programming languages I first choose a non-trivial programming problem and then develop pieces of that system in the new language then go back and re-factor as I learn more. Solving a real problem with the language is the fastest way I have found to gain demonstrated competence in a new language.

I first discover examples of the key things you need to accomplish in any distributed system such as fetching a remote web page, parsing a delimited file, Sorting an array. This document contains links to information I discovered along the way. Let me know of links you think should be added.

Helpful Scala Links

Items that should be considered must Read are prefixed with **.
Items prefixed **# specify recommended study order

Joe’s Complete Examples Scala Code to Download and Render NASA SRTM Digital Elevation Models (DEM) Scala parse almost ISO formatted DateTime with proper timeZone adjustment uses Java.Time Scala example of fetching a string from remote URI, saving results in local file using command line parameters. Similar to curl Scala example to download Yahoo finance stock bar data. Saves each year in separate CSV bar file.	Tutorials 1 Scala Hello World getting started 2 Scala Tutorial by tutorials Point good end to end intro quick. 4 Wiki Scala Intro with examples Scala vs Java Wikibook scala 6 Scala By Example PDF by Martin Odesky 145 pages. Concise Guide to Scala First Steps in Scala for beginning programmers Maps and Lists sets, group By, options, flatten, flatMap Getting started with Scala by udemy. Nice step by step walk-through. Assumes IntelliJ A Tour of Scala bite sized essentials Scala Overview by Martin Odersky 20 pages Scala Tutorial for Java programmers by Michael Schinz 15 pages Scala Guides and Overviews Simple Example Programs abstractTypes, bigInt, complex, for-yield, extnedBuiltIns, implicits, maps, match, primes, sum, varargs	Quick Reference Scala Cheat Sheet Uiowa.edu quick ref Language Comparisons Rosetta Code shows examples of most common programming tasks in many languages including Scala. Compare Scala vs Java Scala for fun Scala Basics for Python programmers Python to Scala gitbook pdf Scala Tutorial for Java Programmers Scala for Java Refugees Style & Best Practices ** Twitter Guide to effective Scala. Nice Rules good starting set. Online Tool to format & Colorize Scala. Generates HTML to allow insert colorized version into web page.
Install Scala Tool-set Most common issues arise from bad version of Java. Install a new JDK first and remove old Java if feasible. JDK 8 or newer Scala SDK Scala IDE based on eclipse Nodepad++ makes easier to run tests from command line Play Framework In Browser Activator supports exploration in browser. Alternative to Scala SDK. Scala-lang Documentation Setting up your preferred IDE ..	Basics Multi Line strings in Scala Scala Operators tutorial If then Else Tutorial Scala Exceptions try catch finally Scala Functions Tutorial Scala for loop comprehensions and for yield Using For-Comprehensions in Scala Iterators explained in detail Blocks within for comprehensions For Expressions Revisited – must read Java Inter-operation Scala fetch URI with Java classes github.. Dependency Injection and @Singleton in play	Data Structures Scala Arrays tutorial includes concatenate array Scala Maps tutorial. Maps are similar to Dictionary Scala Lists Tutorial Object sorting in Scala Merge Sort in Scala very nice and concise implementation. How to merge scala lists Ieterating over Scala Maps using foreach Examples of Sequences, Sets, Maps ..
Files How to append to a file in Scala Append record to end text file rosetta code Read & Write Binary Files in Scala Count lines in text file. Shows dramatic performance difference between different Scala approaches. Scala file reading performance Random Access seekable file access in scala Processing large files in Scala performance rules best practice Handling large data files using Scala and Akka Simple binary file search discussion. Get list of files CSV Parser in Scala github Practical Scala file IO and regular expressions nice example of small file copy snippet. TODO: Recursively scan directory TODO: Detect when File changes Create Directories Recursively Check Directory exists ..	Parsing Scala String Class Docs Scala RegEx Docs Basic Scala Regex matching Parse String convert to Int TODO: Parse string into a object Tokenize a String with multiple spaces. Also shows RE pattern split. Splitting Strings dotNetPerls also shows multiple tokens, split on phrases and ieterated over tokens Splitting Strings Scala Cookbook (Safari online) Parse ISO Time String Parsing Text with Scala using Case Classes for pattern matching NLP Neural Linguistic Parsing with Scala	Web Client Parsing JSON with Play Framwork How to download URI using Scala Scala fetch URI with Java classes github Compare Scala with Java download web pages Scala for fun http get using Sorce.fromURL with timeout and method override Async Page Fetch with Callback paged in chunks this is the way most servlet code that needs to call remote services should handle it especially when making multiple calls simutaneously. wraps java.net.HttpURLConnection TODO: Multiple Async Page Fetch with Promises
O.O. programming Add new methods to existing classes uses implicit conversion technique Adding a method to the string class Implicit Class for extension methods explained Class Casting in Scala uses java asInstanceOf. Named aurguments and default aurguments .. ..	Functional Programming Coursera classes for functional programming principals using Scala For loop with yield builds a new array based on computation or selection in loop.	Reactive Programming Introduction to Reactive programming you have been missing
Command Line Convert args to upper case How to execute System commands in Scala includes redirection output How to build pipeline of external commands in Scala Execute external system commands in Scala including reading command code or result string	Netty Server Getting started Play Web Server 3 Hello World First Play application Learn this early because play contains a lot of libraries you may recreate unless you have learned something about it. Using the Play Console 5 Building a REST JSON service in Play HTTP Routing Play Dynamic routing DSL Advanced routing in play framework Anatomy of Play Application (Directory Structure explained) Play Server Tutorials and templates and seeds. With install directions Pre-configured Play Templates Work with public assets Other Servers Simple HTTP Server in Scala Spray high performance HTTP in Scala	Play Hosting Play Hosting options manual Hosting Companies Play framework hosting at JVM Host hosts under Tomcat as servlet. Host your Scala Play framework web app on Scalingo – push code to Github and they take care of rest. Host Play Framework apps on openShift express and JBOSS Hosting Java apps on the Web Free and Low cost hosting for play framework apps – stack overflow. Lots of noise but a few gems. Elastic Search Hosting Building Web apps often requires search. We can always spin up a AWS instance or a dedicated node from cloudSouth.com but these vendors provide pre-installed elastic search. Hosting Elastic search with Compose Elastic.co managed elastic search hosting Ryft fast search no indexing
Machine Learning Finding K Nearest Neighbors for fun and profit Apache Spark Machine Learning Example in Scala NLP Neural Linguistic Parsing with Scala	..	..
..	, Scala in Browser / Client Side Scala tryScala Interactive execution of Scala in applet on browser Scala in browser getting started with Scala.js. Compiles scala to javascript that runs in browser. TODO: Ajax example in scala.js TODO: DOM find element in scala.js TODO: DOM add element in scala.js TODO: Modify CSS dynamically TODO: Inserted generated HTML into DIV.	Groups and Blogs Googles Scala users group
..	,	,Sample of using from URL direct copy to fix binary issues with URL file donwload
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We provide consulting services with a specialty in solving complex distributed problems. Please contact us if you need help.

Overcome Class not found when compiling from command line.

If you compile a class or package from command line Scala will not find it unless you add -classpash . to your command line. This tells scala to search your current directory.

 Example:    scala -classpath . readHGTElevationGenJPG.scala

exSampleLibrary.scala

 package mylibs.sample {
 object util { 
 def printAString( aStr : String) = {
 println("printAString() " + aStr )
 }
 }
}

exSampleLibraryTest.scala

import mylibs.sample
sample.util.printAString("I am a string")

exSampleLibraryTest.bat

call scalac exSampleLibrary.scala

echo Using implied class path from enviornment variable
echo Seems to fail with error can not find import under
echo some conditions but have not been able to reliably 
echo predict when it will fail.

call scala exSampleLibraryTest.scala

echo Now try it with our class path explicit  By adding
echo the class path it manually it never seems to fail
scala -classpath . exSampleLibraryTest.scala

NOTE: I use the mylibs. or something similar to keep all the class files junk generated by the compliler out of my main source directories. It also makes it easy to avoid saving those binaries with the git ignore file.

I tend to distrust IDE. Or more specifically i like to be able to build everything explicitly and know what the underlying tools are doing before depending and build packages. I blew a a couple hours on this because I expected the scala command line to search the java CLASSPATH for resolving module names. I always have my java CLASSPATH set with .;./lib;..;../lib;../..;../../lib so I can have sub projects that depend on more general library modules. I would have expected scala to find my locally compiled modules this way but it didn’t.

Random Notes

There is no char in Scala they are treated as strings

JSON LIKE Hash Map

  bluex = { 
     'name': 'Johny Blue',
     'weight' : 170,
     'height' : 62 
   }

Define class constructor values with var to allow mutable elements as class attributes.

Play Routing

play – Accessing files saved in the public directory

Using the Standard play 2.4 seed you can add a new file under the /public directory such as sample.txt This can be retrieved using the URI: http://127.0.0.1:9000/assets/sample.txt without having to change the routes file.

play – Creating a Alias to Directory inside of the project

Creating an alias for the public directory under conf/routes add the line GET /s/*file controllers.Assets.versioned(path=”/public”, file: Asset) which allows the sample.txt file stored in public/sample.txt to be accessed as http://127.0.0.1:9000/s/sample.txt

play – Creating an alias to file external to the Play application

I used this because I need to reference stock and forex data files that can be hundreds of gigabytes and do not have sufficient storage to duplicate them in different directories for different projects an when running on windows the symbolic link doesn’t work. Add the following to the file conf\router

GET /forex/*file controllers.ExternalAssets.at(path=”/stock/jstrade”, file)

Retrieved the file existing file actions.txt with view-source:http://127.0.0.1:9000/forex/actions.txt

Joe’s Complete Examples

Tutorials

Quick Reference

Language Comparisons

Style & Best Practices

Install Scala Tool-set

Basics

Java Inter-operation

Data Structures

Files

Parsing

Web Client

O.O. programming

..

Functional Programming

Reactive Programming

Command Line

Netty Server

Play Web Server

Other Servers

Play Hosting

Hosting Companies

Elastic Search Hosting

Machine Learning

..

Scala in Browser / Client Side Scala

Groups and Blogs

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