Re.Mark

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Archive for March 2011

TF#I Friday #5 : In which I return to C# for a bit

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In my last post I counted some words using F#, which turned out to require a single, simple line of F#.  When I’d done the same thing before in C# i had iterated over the words and kept a count as I went, which is a typically imperative approach.  So, I wondered if you could apply the functional approach to C# – perhaps using LINQ.  Turns out you can.

Firstly, it’s helpful to have some words to count.  Here’s a simple approach:


string test = "The cat sat on the mat.";
string[] words = test.Split(' ');

(In F# I populated a list of words directly, so there’s an extra line of C# here – largely because I started with my previous C# code.)  Right, now to the counting in one line:


var result = from word in words
             let strippedWord = StripPunctuation(word).ToLower()
             where strippedWord.Length > 0
             group word by strippedWord into grouped
             select new { Word = grouped.Key, Count = grouped.Count() };

You  may have noticed a call to StripPunctuation – a utility function I had in my previous C# code.  Here it is (declared static as I was running it in a console application:


private static string StripPunctuation(string word)
{
    string result = word;
    if (result.Length > 0)
    {
        if (char.IsPunctuation(result[0]))
        {
            result = result.TrimStart(result[0]);
        }
        if (result.Length > 0)
        {
            if (char.IsPunctuation(result[result.Length - 1]))
            {
                result = result.TrimEnd(result[result.Length - 1]);
            }
        }
    }
    return result;
}

And now, with a little sprinkling of dynamic capability, outputting the results to the console:


foreach (dynamic entry in result)
{
    Console.WriteLine("{0}\t{1}", entry.Word, entry.Count);
}

So it is possible to apply the more functional approach courtesy of LINQ, although there’s still more code than I had in F#.  The C# is doing a couple of extra things (it strips out punctuation and is case insensitive) – but the point isn’t really the comparison between the two examples so much as the fact that by grasping some functional concepts can result in a change to your C# – which is a good reason to learn some F#.

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Written by remark

March 25, 2011 at 5:43 pm

Posted in .NET, c#, Development, F#, Languages

TF#I Friday #4 : In which I count some words

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For a recent MSDN Flash article I wrote some simple code to calculate word frequency in C#.  As I get to grips with F#, I’m learning that the most rewarding but also the most difficult aspect is to think in a more functional way.  To count words in an imperative style (as I did in my C# example) I would iterate through a collection of words and keep a running count.  And, of course, you could write code in F# to do that.  But what would be the point?  How about approaching it in a different fashion?  So, with those questions in mind, I fired up Visual Studio and went about trying to bend my brain into a more F# like shape.  One of the things I like about F# is F# Interactive – a REPL which makes trying out and learning F# (as well as prototyping) easy – so that was where I started.  First thing I needed to do was to create a list of words (since at this stage I’m concerned simply with calculating frequency and not reading files or strings.)  It’s fairly simple to do that in F#:

let words = ["the"; "cat"; "sat"; "on"; "the"; "mat"];;

(the double semicolons are signal to F# Interactive the completion of a statement.)  After reading a bit about processing sequences in F#, I spotted that there is a function to count elements in a list – it can easily be used against the whole list like this:

let count = words |> Seq.countBy(fun x -> x);;

The countBy function takes a function to generate a key – in this case we can use each individual word.  To see if that has worked, we can print out the contents of the result:

printfn "%A" count;;

And in this case, I got the following result:

seq [("the", 2); ("cat", 1); ("sat", 1); ("on", 1); …]
val it : unit = ()

Which means it worked as intended.  There’s work to be done to make it the equivalent of the C# code, but the core counting is implemented in one line of code.

Written by remark

March 4, 2011 at 5:09 pm

Posted in .NET, c#, Development, F#, Languages