Before getting started with Machine Learning in F# Interactive it’s best to prepare it for large datasets so you don’t get blindsided with strange errors when you happen to cross the line. The good news is it’s a simple process that should only take a few minutes.

The first step is to go into the configuration and set fsi to 64-bit. It’s only matter of changing a boolean value buried deep in the Visual Studio settings. First, Go into Tools->Settings.

Then find the “F# Tools” section on the left and select the “F# Interactive” subsection.

Finally, set “64-bit F# Interactive” to true and click OK.

What this does is set Visual Studio to use “FsiAnyCPU.exe” for the F# Interactive window instead of 32-bit “Fsi.exe”.

Now, after we restart Visual Studio, your F# Interactive is running with as many bits as your operating system can handle. However, if we want to support really big matrices we’re going to need to go a bit further. If we want really large arrays, that is greater than 2 gigabytes, we’re going to need to fiddle with the F# Interactive application config and enable the “gcAllowVeryLargeObjects” attribute.

For .NET 4.5 on Windows 7, Windows 8 and Windows Sever 2008R2 the standard directory for both the fsi exeuctables and their application configs is:

“C:\Program Files (x86)\Microsoft SDKs\F#\3.0\Framework\v4.0″

Navigate there and open “FsiAnyCPU.exe.config” in your favorite text editor. Then just add:

<gcAllowVeryLargeObjects enabled=”true” />

When you’re done it should look like:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <runtime>
    <gcAllowVeryLargeObjects enabled="true" />
    <legacyUnhandledExceptionPolicy enabled="true" />
    <assemblyBinding 
      xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity
          name="FSharp.Core"
          publicKeyToken="b03f5f7f11d50a3a"
          culture="neutral"/>
        <bindingRedirect
          oldVersion="2.0.0.0"
          newVersion="4.3.0.0"/>
        <bindingRedirect
          oldVersion="4.0.0.0"
          newVersion="4.3.0.0"/>
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
</configuration>

And there you have it. Your F# Interactive can now handle large datasets and loading external 64-bit native libraries.