Tuesday, November 30, 2010

Project Chadwick #1- Willie McCovey’s Career Batting Average

Before I get started on this post if you aren't familiar with Project Chadwick here's a quick overview.

I have started this off with an easy problem, calculating Willie McCovey’s career batting average.  Starting this way made it easy for me to concentrate on learning enough to get something running without taking up too much time.   In this post I will tackle a solution in all four of the languages I’m interested in:  Erlang, F#, Ruby and Objective-C.  As time goes on and the code for each solution grows I will probably move to a single post per language for each problem. 

A little background on my experience with the languages I have chosen.  I have been using Ruby for a few months now.  We have converted our build process from MSBuild over to rake and albacore, used rails to do a proof of concept, and written other Ruby scripts to do administrative things.  However with Erlang, F# and Objective-C I am truly learning them as I go through this process.  If you see room for improvement in any of my solutions please feel free to share them.

As for my setup for creating these solutions I am running the F# on Windows 7 and all other languages on Linux.  The F# may also move to Linux once I get my F# environment setup there.  With that said lets get started!

Batting Average Formula: Hits/At Bats

Languages: F#, Erlang, Ruby and Objective-C

Data: download from here.

Without further ado here are the functional languages (F# and Erlang) solutions:

Erlang Solution

A quick overview of the syntax you see in the script. First %% are used to write comments.  Erlang requires all variables start with a capital letter.  Also once a variable has been assigned a value it cannot be changed. Function bodies are preceded by the –> sign. For functions that have multi line bodies commas are used to indicate an end of line.  The main function is an example of this.  The last line of the function’s body has a period as its last character.

The first line of the file is setting up so I can run this like any other script in Linux.  After the comment lines the sum functions are defined.  Each function is uniquely identified by the module it appears in, the name and its ‘arity’.  What is arity? Arity is the number of arguments the function has.  In our cause the first sum method has an arity of 2 and the second has an arity of 1. The sum functions are two distinct functions they have nothing to do with each other.  The sum functions are used to total up the career hits and at bats.

The main function  does what you’d expect it to do, it is where the batting average is calculated.  The first two code lines set up lists of the career hits and career at bats for McCovey.  I had wanted to use tuples here but I was not getting the correct average using it.  So I junked the tuples and went with something I knew would work.  The last line of main simply prints out “Willie McCovey’s career bating average is 0.270” .  The place holder is replaced with the result of sum(Hits)/sum(Abs).  The function signature for the io:format method looks like this:

io:format([IoDevice,] Format, Data) 

The io is what module houses the format function.  format’s parameters are: IoDevice if left out stdout is used. If we were writing to a file we would pass the file handle as the IoDevice. Format is the string with as many placeholders as you need.  The Data parameter is used to replace the placeholders.  The number of items in the Data list must equal the number of placeholders in the string.

The Erlang solution was quick and to the point 

The F# Solution

F# is a .NET functional language.  I am learning this language in hopes that I can use it to do some more complicated comparisons quicker than I could in C#.  With that said, lets jump into the F# solution.

As you can see it is very similar to the Erlang code.  With F# we define the sum function in one line but it handles the same two situations as the Erlang sum functions do.  Head and tail have the same meaning as H and T do in Erlang. It adds the head to the result of the recursive call on sum.  When sum is at the end of the list or receives an empty list it returns zero. A real difference between the Erlang and F# code is that we have to add the rec keyword to the function’s definition to indicate that this is a recursive function.  The printfn method is called to write the results out to stdout.  Notice that in the calls to sum we do not use parenthesis that is because parenthesis are used for precedence operations, to create pairs and tuples and to denote a parameter of type void.  It takes a little getting use to not using parenthesis in function calls but after you do, the code seems a little cleaner.

The Ruby Solution

Now that we have the functional languages done lets move to something a little more familiar to most of us, object oriented programming.  Although this Ruby solution really doesn’t do much with objects. 

For this script I’ve combined the hits and at bats for each season as an array.  So the hits_ab array is an array of arrays.  Next I initialize a variable to store the total hits and one for the total at bats.  These are set to 0.0 so that when I do the division I do not have to convert the sums to floats using the to_f method. 

The each loop is one of the cool features of Ruby, the use of blocks.  The do …end is a block of code that is passed to the each method as a parameter.  In our case the block is taking each of the arrays that are ‘in’ the hit_ab array and storing the first entry in the h variable and the second entry in the ab variable. 

The last line prints the results to stdout after formatting the average.  The #{} in a ruby string is how you put the value of a variable, method call, or in our case the formatted results of the division into a string. 

The Objective-C Solution

Ok, I have to admit this up front, I’m really learning this language as I go through this process.  This is my weakest of the 4 languages here, so please help feel free to guide me into the proper way of doing things if you see something wrong.

Most of this solution is really straight C code but it gets the job done.  The first Objective-C or obj-c related line is the #include<Foundation/Foundation.h>.  This header file is the base header file for obj-c. The second obj-c line is the NSAutoreleasePool line.  The NSAutoreleasePool object is to support Cocoa’s, an Apple development framework, reference counted memory management system.  All of the objects in the pool are sent a release message when the NSAutoreleasePool' object is sent the drain message.  In the above code the drain message is sent in the [pool drain]; line.

More on the NSAutoreleasePool line

In this line of code NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; there are some interesting things going on.  Lets look at the inner bits of code [NSAutoreleasePool alloc].  In obj-c method calls are done like so [object methodname].  What inner call is doing is allocating the memory that the *pool pointer will point to.  When the new object is returned we call its init method which is its constructor call.  Now we have a fully initialized NSAutoreleasePool object.



Admittedly this was an easy problem to solve so the code for each language was very similar. It also hints that the functional languages tend to require less code to do the same thing.  Ruby is in between the functional and Objective-C code.  I’m sure I could make the Ruby solution look even more like the functional languages if I put more time into it.

Remember, I am learning these languages as I go so if you see something I’m doing completely wrong or not as gracefully as I could don’t hesitate to pass it along.  I would greatly appreciate it.  As these problems get more complicated and the code required grows, I will do each language one at a time.

Up next: I will find the top 5 on base percentages since the Giants moved to San Francisco.

Language Resources

For additional information on these languages you can visit these sites:

Erlang:        http://www.erlang.org/
F#:              The F# Survival Guide
Objective-C: Learning Objective-C: A Primer
Ruby:          http://www.ruby-lang.org/

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