Added another dataflow example from the wiki.

Author: jdantonio

doc/dataflow_top_stock_calc.md

@@ -0,0 +1,84 @@
+This program determines which stock had the highest price in a given year.
+It as an example from chapter 1 "Introduction", section 1.2 "What's Scala?" of the book
+[Programming Scala: Tackle Multi-Core Complexity on the Java Virtual Machine](http://pragprog.com/book/vsscala/programming-scala).
+
+## What It Does
+
+This program takes a list of one or more stock symbols and a year. It then concurrently
+obtains the relevant stock data from Yahoo's iChart service for each symbol. Once all
+the data has been retrieved the program determines which stock had the highest year-end
+closing price.
+
+* A sample of the data can be downloaded [here](http://ichart.finance.yahoo.com/table.csv?s=AAPL&a=11&b=01&c=2008&d=11&e=31&f=2008&g=m).
+
+#### The Ruby Code
+
+```ruby
+require 'concurrent'
+require 'open-uri'
+
+def get_year_end_closing(symbol, year)
+  uri = "http://ichart.finance.yahoo.com/table.csv?s=#{symbol}&a=11&b=01&c=#{year}&d=11&e=31&f=#{year}&g=m"
+  data = open(uri) {|f| f.collect{|line| line.strip } }
+  price = data[1].split(',')[4]
+  price.to_f
+  [symbol, price.to_f]
+end
+
+def get_top_stock(symbols, year, timeout = 5)
+  stock_prices = symbols.collect{|symbol| Concurrent::dataflow{ get_year_end_closing(symbol, year) }}
+  Concurrent::dataflow(*stock_prices) { |*prices|
+    prices.reduce(['', 0.0]){|highest, price| price.last > highest.last ? price : highest}
+  }.value(timeout)
+end
+
+symbols = ['AAPL', 'GOOG', 'IBM', 'ORCL', 'MSFT']
+year = 2008
+
+top_stock, highest_price = get_top_stock(symbols, year)
+
+puts "Top stock of #{year} is #{top_stock} closing at price $#{highest_price}"
+```
+
+#### The Scala Code
+
+```scala
+//START:PART1
+import scala.actors._
+import Actor._
+
+val symbols = List( "AAPL", "GOOG", "IBM", "JAVA", "MSFT")
+val receiver = self
+val year = 2008
+
+symbols.foreach { symbol =>
+  actor { receiver ! getYearEndClosing(symbol, year) }
+}
+
+val (topStock, highestPrice) = getTopStock(symbols.length)
+
+printf("Top stock of %d is %s closing at price %f\n", year, topStock, highestPrice)
+//END:PART1
+
+//START:PART2    
+def getYearEndClosing(symbol : String, year : Int) = {
+  val url = "http://ichart.finance.yahoo.com/table.csv?s=" +
+    symbol + "&a=11&b=01&c=" + year + "&d=11&e=31&f=" + year + "&g=m"
+    
+  val data = io.Source.fromURL(url).mkString
+  val price = data.split("\n")(1).split(",")(4).toDouble  
+  (symbol, price)
+} 
+//END:PART2    
+
+//START:PART3
+def getTopStock(count : Int) : (String, Double) = {
+  (1 to count).foldLeft("", 0.0) { (previousHigh, index) =>
+    receiveWithin(10000) {
+      case (symbol : String, price : Double) =>
+        if (price > previousHigh._2) (symbol, price) else previousHigh
+    }
+  }
+} 
+//START:PART3
+```