To be honest this is well documented on NDpend’s web site – Defining a procedure in a query.
A previous post on CQLinq covered using a query to filter types for use in another CQLinq query. An alternate might be to create your own filter function.
To create a function in CQLinq we can simply create a Func variable and then create the code that is called when the variable is used, for example
let Ignore = new Func<IField, bool>(f => f.ParentAssembly.Name == "ThirdPartAssembly" )
Now to use the function we simply use it like this
from f in JustMyCode.Fields where !Ignore(f)