Mathias Brandewinder on .NET, F#, VSTO and Excel development, and quantitative analysis / machine learning.
by Mathias 30. March 2015 16:34

In our previous post, we looked at James McCaffrey’s code, “Gradient Descent Training Using C#” from MSDN magazine, and took a stab at rewriting the first part in F#, to clarify a bit the way the dataset was created. Today, we’ll dive in the second block, which implements the logistic regression using gradient descent. Again, we won’t discuss why the algorithm works – the article does a pretty good job at that – and focus instead purely on the F# / C# conversion part.

Let’s begin by taking a look at the core of the C# code, which lives in the LogisticClassifier class. I took the liberty to do some minor cleanup, and remove some parts which were un-necessary, so as to make it a bit easier to see what is going on:

public class LogisticClassifier
{
    private int numFeatures; // number of x variables aka features
    private double[] weights; // b0 = constant
    private Random rnd;

    public LogisticClassifier(int numFeatures)
    {
        this.numFeatures = numFeatures;
        this.weights = new double[numFeatures + 1]; // [0] = b0 constant
        this.rnd = new Random(0);
    }

    public double[] Train(double[][] trainData, int maxEpochs, double alpha)
    {
        // alpha is the learning rate
        int epoch = 0;
        int[] sequence = new int[trainData.Length]; // random order
        for (int i = 0; i < sequence.Length; ++i)
            sequence[i] = i;

        while (epoch < maxEpochs)
        {
            ++epoch;

            if (epoch % 100 == 0 && epoch != maxEpochs)
            {
                double mse = Error(trainData, weights);
                Console.Write("epoch = " + epoch);
                Console.WriteLine("  error = " + mse.ToString("F4"));
            }

            Shuffle(sequence); // process data in random order

            // stochastic/online/incremental approach
            for (int ti = 0; ti < trainData.Length; ++ti)
            {
                int i = sequence[ti];
                double computed = ComputeOutput(trainData[i], weights);
                int targetIndex = trainData[i].Length - 1;
                double target = trainData[i][targetIndex];

                weights[0] += alpha * (target - computed) * 1; // the b0 weight has a dummy 1 input
                for (int j = 1; j < weights.Length; ++j)
                    weights[j] += alpha * (target - computed) * trainData[i][j - 1];             
            }
        } // while
        return this.weights; // by ref is somewhat risky
    } // Train

    private void Shuffle(int[] sequence)
    {
        for (int i = 0; i < sequence.Length; ++i)
        {
            int r = rnd.Next(i, sequence.Length);
            int tmp = sequence[r];
            sequence[r] = sequence[i];
            sequence[i] = tmp;
        }
    }

    private double Error(double[][] trainData, double[] weights)
    {
        // mean squared error using supplied weights
        int yIndex = trainData[0].Length - 1; // y-value (0/1) is last column
        double sumSquaredError = 0.0;
        for (int i = 0; i < trainData.Length; ++i) // each data
        {
            double computed = ComputeOutput(trainData[i], weights);
            double desired = trainData[i][yIndex]; // ex: 0.0 or 1.0
            sumSquaredError += (computed - desired) * (computed - desired);
        }
        return sumSquaredError / trainData.Length;
    }

    private double ComputeOutput(double[] dataItem, double[] weights)
    {
        double z = 0.0;
        z += weights[0]; // the b0 constant
        for (int i = 0; i < weights.Length - 1; ++i) // data might include Y
            z += (weights[i + 1] * dataItem[i]); // skip first weight
        return 1.0 / (1.0 + Math.Exp(-z));
    }
} // LogisticClassifier

Just from the length of it, you can tell that most of the action is taking place in the Train method, so let’s start there. What we have here is two nested loops. The outer one runs maxEpoch times, a user defined parameter. Inside that loop, we randomly shuffle the input dataset, and then loop over each training example, computing the predicted output of the logistic function for that example, comparing it to a target, the actual  label of the example, which can be 0 or 1, and adjusting the weights so as to reduce the error. We also have a bit of logging going on, displaying the prediction error every hundred outer iteration. Once the two loops are over, we return the weights.

Two things strike me here. First, a ton of indexes are involved, and this tends to obfuscate what is going on; as a symptom, a few comments are needed, to clarify how the indexes work, and what piece of the data is organized. Then, there is a lot of mutation going on. It’s not necessarily a bad thing, but I tend to avoid it as much as possible, simply because it requires keeping more moving parts in my head when I try to follow the code, and also, as McCaffrey himself points out in a comment, because “by ref is somewhat risky”.

As a warm up, let’s begin with the error computation, which is displayed every 100 iterations.  Rather than having to remember in what column the actual expected value is stored, let’s make our life easier, and use a type alias, Example, so that the features are neatly tucked in an array, and the value is clearly separated. We need to compute the average square difference between the expected value, and the output of the logistic function for each example. As it turns out, we have already implemented the logistic function in the first part in the code, so re-implementing it as in ComputeOutput seems like un-necessary work – we can get rid of that part entirely, and simply map every example to the square error, and compute the average, using pattern matching on the examples to separate clearly the features and the expected value:

type Example = float [] * float

let Error (trainData:Example[], weights:float[]) =
    // mean squared error using supplied weights
    trainData
    |> Array.map (fun (features,value) -> 
        let computed = logistic weights features
        let desired = value
        (computed - desired) * (computed - desired))
    |> Array.average

Some of you might argue that this could be made tighter – I can think of at least two possibilities. First, using a Tuple might not be the most expressive approach; replacing it with a Record instead could improve readability. Then, we could also skip the map + average part, and directly ask F# to compute the average on the fly:

type Example = { Features:float[]; Label:float }

let Error (trainData:Example[], weights:float[]) =
    trainData
    |> Array.averageBy (fun example -> 
        let computed = logistic weights example.Features
        let desired = example.Label
        (computed - desired) * (computed - desired))

I will keep my original version the way it is, mostly because we created a dataset based on tuples last times.

We are now ready to hit the center piece of the algorithm. Just like we would probably try to extract a method in C#, we will start extracting some of the gnarly code that lies in the middle:

for (int ti = 0; ti < trainData.Length; ++ti)
{
    int i = sequence[ti];
    double computed = ComputeOutput(trainData[i], weights);
    int targetIndex = trainData[i].Length - 1;
    double target = trainData[i][targetIndex];

    weights[0] += alpha * (target - computed) * 1; // the b0 weight has a dummy 1 input
    for (int j = 1; j < weights.Length; ++j)
        weights[j] += alpha * (target - computed) * trainData[i][j - 1];             
}

Rather than modify the weights values, it seems safer to compute new weights. And because we opted last week to insert a column with ones for the constant feature, we won’t have to deal with the index misalignment, which requires separate handling for b0 and the rest. Instead, we can write an update operation that takes in an example and weights, and returns new weights:

let update (example:Example) (weights:float[]) =
    let features,target = example
    let computed = logistic weights features
    weights 
    |> Array.mapi (fun i w -> 
        w + alpha * (target - computed) * features.[i])

Array.mapi allows us to iterate over the weights, while maintaining the index we are currently at, which we use to grab the feature value at the corresponding index. Alternatively, you could go all verbose and zip the arrays together – or all fancy with a double-pipe and map2 to map the two arrays in one go. Your pick:

Array.zip weights features
|> Array.map (fun (weight,feat) -> 
    weight + alpha * (target - computed) * feat)

(weights,features) 
||> Array.map2 (fun weight feat -> 
    weight + alpha * (target - computed) * feat)

We are now in a very good place; the only thing left to do is to plug that into the two loops. The inner loop is a perfect case for a fold (the Aggregate method in LINQ): given a starting value for weights, we want to go over every example in our training set, and, for each of them, run the update function to compute new weights. For the while loop, we’ll take a different approach, and use recursion: when the epoch reaches maxEpoch, you are done, return the weights, otherwise, keep shuffling the data and updating weights. Let’s put that all together:

let Train (trainData:Example[], numFeatures, maxEpochs, alpha, seed) =
           
    let rng = Random(seed)
    let epoch = 0

    let update (example:Example) (weights:float[]) =
        let features,target = example
        let computed = logistic weights features
        weights 
        |> Array.mapi (fun i w -> 
            w + alpha * (target - computed) * features.[i])

    let rec updateWeights (data:Example[]) epoch weights =
        
        if epoch % 100 = 0 
        then printfn "Epoch: %i, Error: %.2f" epoch (Error (data,weights))
        
        if epoch = maxEpochs then weights
        else
            let data = shuffle rng data
            let weights = 
                data 
                |> Array.fold (fun w example -> update example w) weights
            updateWeights data (epoch + 1) weights
    // initialize the weights and start the recursive update
    let initialWeights = [| for _ in 1 .. numFeatures + 1 -> 0. |]
    updateWeights trainData 0 initialWeights

And that’s pretty much it. We replaced the whole class by a couple of functions, and all the indexes are gone. This is probably a matter of taste and comfort with functional concepts, but in my opinion, this is much easier to follow.

Before trying it out, to make sure it works, I’ll take a small liberty, and modify the Train function. As it stands right now, it returns the final weights, but really, we don’t care about the weights, what we want is a classifier, which is a function that, given an array, will predict a one or a zero. That’s easy enough, let’s return a function at the end instead of weights:

// initialize the weights and start the recursive update
let initialWeights = [| for _ in 1 .. numFeatures + 1 -> 0. |]
let finalWeights = updateWeights trainData 0 initialWeights
let classifier (features:float[]) = 
    if logistic finalWeights features > 0.5 then 1. else 0.
classifier

We can now wrap it up, and see our code in action:

printfn "Begin Logistic Regression (binary) Classification demo"
printfn "Goal is to demonstrate training using gradient descent"

let numFeatures = 8 // synthetic data
let numRows = 10000
let seed = 1

printfn "Generating %i artificial data items with %i features" numRows numFeatures    
let trueWeights, allData = makeAllData(numFeatures, numRows, seed)

printfn "Data generation weights:"
trueWeights |> Array.iter (printf "%.2f ")
printfn ""

printfn "Creating train (80%%) and test (20%%) matrices"
      
let trainData, testData = makeTrainTest(allData, 0)
printfn "Done"

let maxEpochs = 1000
let alpha = 0.01

let classifier = Train (trainData,numFeatures,maxEpochs,alpha,0)

let accuracy (examples:Example[]) = 
    examples 
    |> Array.averageBy (fun (feat,value) -> 
        if classifier feat = value then 1. else 0.)

accuracy trainData |> printfn "Prediction accuracy on train data: %.4f"
accuracy testData |> printfn "Prediction accuracy on test data: %.4f"

We used a small trick to compute the accuracy – we mark every correct call as a one, every incorrect one as a zero, which, when we compute the average, gives us directly the proportion of cases that were called correctly. On my machine, I get the following output:

> 
Prediction accuracy on train data: 0.9988
Prediction accuracy on test data: 0.9980

Looks good enough to me, the implementation seems to be working. The whole code presented here is available as a gist here. I’ll leave it at that for now (I might revisit it later, and try to make this work with DiffSharp at some point, if anyone is interested) – feel free to ask questions, or drop me a comment on Twitter!

by Mathias 22. March 2015 17:27

I will admit it, I got a bit upset by James McCaffrey’s column in MSDN magazine this month, “Gradient Descent Training Using C#”. While the algorithm explanations are quite good, I was disappointed by the C# sample code, and kept thinking to myself “why oh why isn’t this written in F#”. This is by no means intended as a criticism of C#; it’s a great language, but some problems are just better suited for different languages, and in this case, I couldn’t fathom why F# wasn’t used.

Long story short, I just couldn’t let it go, and thought it would be interesting to take that C# code, and do a commented rewrite in F#. I won’t even go into why the code does what it does – the article explains it quite well – but will instead purely focus on the implementation, and will try to keep it reasonably close to the original, at the expense of some additional nifty things that could be done.

The general outline of the code follows two parts:

  • Create a synthetic dataset, creating random input examples, and computing the expected result using a known function,
  • Use gradient descent to learn the model parameters, and compare them to the true value to check whether the method is working.

You can download the original C# code here. Today we’ll focus only on the first part, which is mainly contained in two methods, MakeAllData and MakeTrainTest:

static double[][] MakeAllData(int numFeatures, int numRows, int seed)
{
  Random rnd = new Random(seed);
  double[] weights = new double[numFeatures + 1]; // inc. b0
  for (int i = 0; i < weights.Length; ++i)
    weights[i] = 20.0 * rnd.NextDouble() - 10.0; // [-10.0 to +10.0]

  double[][] result = new double[numRows][]; // allocate matrix
  for (int i = 0; i < numRows; ++i)
    result[i] = new double[numFeatures + 1]; // Y in last column

  for (int i = 0; i < numRows; ++i) // for each row
  {
    double z = weights[0]; // the b0 
    for (int j = 0; j < numFeatures; ++j) // each feature / column except last
    {
      double x = 20.0 * rnd.NextDouble() - 10.0; // random X in [10.0, +10.0]
      result[i][j] = x; // store x
      double wx = x * weights[j + 1]; // weight * x 
      z += wx; // accumulate to get Y
    }
    double y = 1.0 / (1.0 + Math.Exp(-z));
    if (y > 0.55)  // slight bias towards 0
      result[i][numFeatures] = 1.0; // store y in last column
    else
      result[i][numFeatures] = 0.0;
  }
  Console.WriteLine("Data generation weights:");
  ShowVector(weights, 4, true);

  return result;
}

MakeAllData takes a number of features and rows, and a seed for the random number generator so that we can replicate the same dataset repeatedly. The dataset is represented as an array of array of doubles. The first columns, from 0 to numFeatures – 1, contain random numbers between –10 and 10. The last column contains a 0 or a 1. What we are after here is a classification model: each row can take two states (1 or 0), and we are trying to predict them from observing the features. In our case, that value is computed using a logistic model: we have a set of weights (which we also generate randomly), corresponding to each feature, and the output is

logistic [ x1; x2; … xn ] = 1.0 / (1.0 + exp ( - (w0 * 1.0 + w1 * x1 + w2 * x2 + … + wn * xn))

Note that w0 plays the role of a constant term in the equation, and is multiplied by 1.0 all the time. This is adding some complications to a code where indices are already flying left and right, because now elements in the weights array are mis-aligned by one element with the elements in the features array. Personally, I also don’t like adding another column to contain the predicted value, because that’s another implicit piece of information we have to remember.

In that frame, I will make two minor changes here, just to keep my sanity. First, as is often done, we will insert a column containing just 1.0 in each observation, so that the weights and features are now aligned. Then, we will move the 0s and 1s outside of the features array, to avoid any ambiguity.

Good. Instead of creating a Console application, I’ll simply go for a script. That way, I can just edit my code and check live whether it does what I want, rather than recompile and run every time.

Let’s start with the weights. What we are doing here is simply creating an array of numFeatures + 1 elements, populated by random values between –10.0 and 10.0. We’ll go a bit fancy here: given that we are also generating random numbers the same way a bit further down, let’s extract a function that generates numbers uniformly between a low and high value:

let rnd = Random(seed)
let generate (low,high) = low + (high-low) * rnd.NextDouble()
let weights = Array.init (numFeatures + 1) (fun _ -> generate(-10.0,10.0))

The next section is where things get a bit thornier. The C# code creates an array, then populates it row by row, first filling in the columns with random numbers, and then applying the logistic function to compute the value that goes in the last column. We can make that much clearer, by extracting that function out. The logistic function is really doing 2 things:

  • first, the sumproduct of 2 arrays,
  • and then, 1.0/(1.0 + exp ( – z ).

That is easy enough to implement:

let sumprod (v1:float[]) (v2:float[]) =
    Seq.zip v1 v2 |> Seq.sumBy (fun (x,y) -> x * y)

let sigmoid z = 1.0 / (1.0 + exp (- z))

let logistic (weights:float[]) (features:float[]) =
    sumprod weights features |> sigmoid

We can now use all this, and generate a dataset by simply first creating rows of random values (with a 1.0 in the first column for the constant term), applying the logistic function to compute the value for that row, and return them as a tuple:

open System

let sumprod (v1:float[]) (v2:float[]) =
    Seq.zip v1 v2 |> Seq.sumBy (fun (x,y) -> x * y)

let sigmoid z = 1.0 / (1.0 + exp (- z))

let logistic (weights:float[]) (features:float[]) =
    sumprod weights features |> sigmoid

let makeAllData (numFeatures, numRows, seed) =

    let rnd = Random(seed)
    let generate (low,high) = low + (high-low) * rnd.NextDouble()
    let weights = Array.init (numFeatures + 1) (fun _ -> generate(-10.0,10.0))
    
    let dataset = 
        [| for row in 1 .. numRows ->
            let features = 
                [|  
                    yield 1.0 
                    for feat in 1 .. numFeatures -> generate(-10.0,10.0) 
                |]
            let value = 
                if logistic weights features > 0.55 
                then 1.0 
                else 0.0
            (features, value)
        |]

    weights, dataset

Done. Let’s move to the second part of the data generation, with the MakeTrainTest method. Basically, what this does is take a dataset, shuffle it, and split it in two parts, 80% which we will use for training, and 20% we leave out for validation.

static void MakeTrainTest(double[][] allData, int seed,
  out double[][] trainData, out double[][] testData)
{
  Random rnd = new Random(seed);
  int totRows = allData.Length;
  int numTrainRows = (int)(totRows * 0.80); // 80% hard-coded
  int numTestRows = totRows - numTrainRows;
  trainData = new double[numTrainRows][];
  testData = new double[numTestRows][];

  double[][] copy = new double[allData.Length][]; // ref copy of all data
  for (int i = 0; i < copy.Length; ++i)
    copy[i] = allData[i];

  for (int i = 0; i < copy.Length; ++i) // scramble order
  {
    int r = rnd.Next(i, copy.Length); // use Fisher-Yates
    double[] tmp = copy[r];
    copy[r] = copy[i];
    copy[i] = tmp;
  }
  for (int i = 0; i < numTrainRows; ++i)
    trainData[i] = copy[i];

  for (int i = 0; i < numTestRows; ++i)
    testData[i] = copy[i + numTrainRows];
}

Again, there is a ton of indexing going on, which in my old age I find very hard to follow. Upon closer inspection, really, the only thing complicated here is the Fischer-Yates shuffle, which takes an array and randomly shuffles the order. The rest is pretty simply – we just want to shuffle, and then split into two arrays. Let’s extract the shuffle code (which happens to also be used and re-implemented later on):

let shuffle (rng:Random) (data:_[]) =
    let copy = Array.copy data
    for i in 0 .. (copy.Length - 1) do
        let r = rng.Next(i, copy.Length)
        let tmp = copy.[r]
        copy.[r] <- copy.[i]
        copy.[i] <- tmp
    copy

We went a tiny bit fancy again here, and made the shuffle work on generic arrays; we also pass in the Random instance we want to use, so that we can control / repeat shuffles if we want, by passing a seeded Random. Does this work? Let’s check in FSI:

> [| 1 .. 10 |] |> shuffle (Random ());;
val it : int [] = [|6; 7; 2; 10; 8; 5; 4; 9; 3; 1|]

Looks reasonable. Let’s move on – we can now implement the makeTrainTest function.

let makeTrainTest (allData:_[], seed) =

      let rnd = Random(seed)
      let totRows = allData.Length
      let numTrainRows = int (float totRows * 0.80) // 80% hard-coded

      let copy = shuffle rnd allData
      copy.[.. numTrainRows-1], copy.[numTrainRows ..]

Done. A couple of remarks here. First, F# is a bit less lenient than C# around types, so we have to be explicit when converting the number of rows to 80%, first to float, then back to int. As an aside, this used to annoy me a bit in the beginning, but I have come to really like having F# as this slightly psycho-rigid friend who nags me when I am taking a dangerous path (for instance, dividing two integers and hoping for a percentage).

Besides that, I think the code is markedly clearer. The complexity of the shuffle has been nicely contained, and we just have to slice the array to get a training and test sets. As an added bonus, we got rid of the out parameters, and that always feels nice and fuzzy.

I’ll leave it at for today; next time we’ll look at the second part, the learning algorithm itself. Before closing shop, let me make a couple of comments. First, the code is a tad shorter, but not by much. I haven’t really tried, and deliberately made only the changes I thought were needed. What I like about it, though, is that all the indexes are gone, except for the shuffle. In my opinion, this is a good thing. I find it difficult to keep it all in my head when more than one index is involved; when I need to also remember what columns contain special values, I get worried – and just find it hard to figure out what is going on. By contrast, I think makeTrainTest, for instance, conveys pretty directly what it does. makeAllData, in spite of some complexity, also maps closely the way I think about my goal: “I want to generate rows of inputs” – this is precisely what the code does. There is probably an element of culture to it, though; looping over arrays has a long history, and is familiar to every developer, and what looks readable to me might look entirely weird to some.

Easier, or more complicated than before? Anything you like or don’t like – or find unclear? Always interested to hear your opinion! Ping me on Twitter if you have comments.

by Mathias 26. January 2013 19:08

Phil Trelford recently released Foq, a small F# mocking library (with a very daring name). If most of your code is in F#, this is probably not a big deal for you, because the technique of mocking isn’t very useful in F# (at least in my experience). On the other hand, if your goal is to unit test some C# code in F#, then Foq comes in very handy.

So why would you want to write your unit tests in F# in the first place?

Let’s start with some plain old C# code, like this:

namespace CodeBase
{
    using System;

    public class Translator
    {
        public const string ErrorMessage = "Translation failure";

        private readonly ILogger logger;
        private readonly IService service;

        public Translator(ILogger logger, IService service)
        {
            this.logger = logger;
            this.service = service;
        }

        public string Translate(string input)
        {
            try
            {
                return this.service.Translate(input);
            }
            catch (Exception exception)
            {
                this.logger.Log(exception);
                return ErrorMessage;
            }
        }
    }

    public interface ILogger
    {
        void Log(Exception exception);
    }

    public interface IService
    {
        string Translate(string input);
    }
}
We have a class, Translator, which takes 2 dependencies, a logger and a service. The main purpose of the class is to Translate a string, by calling the service. If the call succeeds, we return the translation, otherwise we log the exception and return an arbitrary error message.

This piece of code is very simplistic, but illustrates well the need for Mocking. If I want to unit test that class, there are 3 things I need to verify:

  • when the translation service succeeds, I should receive whatever the service says is right,
  • when the translation service fails, I should receive the error message,
  • when the translation service fails, the exception should be logged.

In standard C#, I would typically resort to a Mocking framework like Moq or NSubstitute to test this. What the framework buys me is the ability to create cheaply a fake implementation for the interfaces, setup their behavior to whatever my scenario is (“stubbing”), and in the case of the logger, where I can’t observe through state whether the exception has been logged, verify that the proper call has been made (“mocking”).

This is how my test suite would look:

namespace MoqTests
{
    using System;
    using CodeBase;
    using Moq;
    using NUnit.Framework;

    [TestFixture]
    public class TestsTranslator
    {
        [Test]
        public void Translate_Should_Return_Successful_Service_Response()
        {
            var input = "Hello";
            var output = "Kitty";

            var service = new Mock<IService>();
            service.Setup(s => s.Translate(input)).Returns(output);

            var logger = new Mock<ILogger>();

            var translator = new Translator(logger.Object, service.Object);

            var result = translator.Translate(input);

            Assert.That(result, Is.EqualTo(output));
        }

        [Test]
        public void When_Service_Fails_Translate_Should_Return_ErrorMessage()
        {
            var service = new Mock<IService>();
            service.Setup(s => s.Translate(It.IsAny<string>())).Throws<Exception>();

            var logger = new Mock<ILogger>();

            var translator = new Translator(logger.Object, service.Object);

            var result = translator.Translate("Hello");

            Assert.That(result, Is.EqualTo(Translator.ErrorMessage));
        }

        [Test]
        public void When_Service_Fails_Exception_Should_Be_Logged()
        {
            var error = new Exception();
            var service = new Mock<IService>();
            service.Setup(s => s.Translate(It.IsAny<string>())).Throws(error);

            var logger = new Mock<ILogger>();

            var translator = new Translator(logger.Object, service.Object);

            translator.Translate("Hello");

            logger.Verify(l => l.Log(error));
        }
    }
}

More...

by Mathias 1. December 2012 13:55

I have been obsessing about the following idea lately – what if I could run a FSI session from within Excel? The motivation behind this is double. First, one thing Excel is good at is creating and formatting charts. If I could use F# for data manipulation, and Excel for data visualization, I would be a happy camper. Then, I think F# via FSI could provide an interesting alternative for Excel automation. I’d much rather leverage existing .NET libraries to, say, grab data from the internet, than write some VBA to do that – and the ability to write live code in FSI would be less heavy handed that VSTO automation, and closer to what people typically do in Excel, that is, explore data. Having the ability to execute F# scripts would be, at least for me, very useful.

Seeing Tim Robinson’s awesome job with FsNotebook.net kicked me out of procrastination. Even though FsNotebook is still in early development, it provides a very nice user experience – on the web. If something that nice can be done on the web, it should be feasible on a local machine.

As an aside, Tim is looking for feedback and input on FsNotebook – go try it out, it’s really fun:

Anyways – this is the grand plan, now we need to start with baby steps. If I want to embed FSI in Excel (presumably via a VSTO add-in), I need a way to talk to FSI from .NET, so that I can create a Session and send arbitrary strings of code to be evaluated.

As usual, StackOverflow provided two good starting points (this answer, and this answer) – so I set out to look into the Process class, which I didn’t know much about, and attempted to spawn a FSI.EXE process, redirecting input and output. Turns out it’s not overly complicated – here are the 34 lines of code I ended up with so far (see it on GitHub):

namespace ClearLines.FsiRunner

open System.Diagnostics

type public FsiSession(fsiPath: string) =

    let info = new ProcessStartInfo()
    let fsiProcess = new Process()

    do
        info.RedirectStandardInput <- true
        info.RedirectStandardOutput <- true
        info.UseShellExecute <- false
        info.CreateNoWindow <- true
        info.FileName <- fsiPath

        fsiProcess.StartInfo <- info

    [<CLIEvent>]
    member this.OutputReceived = fsiProcess.OutputDataReceived

    [<CLIEvent>]
    member this.ErrorReceived = fsiProcess.ErrorDataReceived

    member this.Start() =
        fsiProcess.Start()
        fsiProcess.BeginOutputReadLine()

    member this.AddLine(line: string) =
        fsiProcess.StandardInput.WriteLine(line)

    member this.Evaluate() =
        this.AddLine(";;")
        fsiProcess.StandardInput.Flush()

This is a fairly straightforward class. The constructor expects the path to FSI.EXE, and sets up the process in the constructor (the do block) to run headless and redirect the stream of inputs and outputs. Start() simply starts the process, and begins reading asynchronously the output of FSI, AddLine(line) is used to add an arbitrary string of F# code, and Evaluate() sends all lines currently buffered to FSI for evaluation – and flushes the buffer. The 2 events OutputReceived and ErrorReceived are provided for the client to listen to the FSI results.

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by Mathias 18. December 2011 14:59

I spent some time this week putting together an example illustrating how to use Bumblebee from C# code. I figured it would be more exciting to have a graphical representation of the bee colony working on the traveling salesman problem, so I put together a small WPF application which creates a random set of cities, and displays the improvements live as they are found by the algorithm.

Here is a screen capture of the first 10 seconds of a 100-cities problem:

Bumblebee working on 100 cities

The source code for the example is available in the current head revision, under the TspDemo.CSharp project; I’ll push an “official” downloadable version as soon as I have time for some cleanup. Note that, besides a reference to Bumblebee, a reference to FSharp.Core 4.0 is required – the rest is all pure C#.

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