Add more documentation to TypedPipe

Sadly, some of TypedPipe had no scaladoc.
Feel free to add those. Please omit the ordering comment or at least say
that TypedPipes semantically are unordered (sumByLocalKeys shuffles key
order, for instance).



On Thu, Dec 4, 2014 at 9:16 PM, Gabriel Gonzalez <notifications@github.com>
wrote:

> In scalding-core/src/main/scala/com/twitter/scalding/typed/TypedPipe.scala:
>
> >    def cross[U](tiny: TypedPipe[U]): TypedPipe[(T, U)]
> >
> > +  /**
> > +   * This is the fundamental mapper operation. Each item is feed to the input
> > +   * function. The result is iterated once and passed to the next step in the
>
> An equation (or four) is worth a thousand words:
>
> p flatMap { _ => empty } = empty
>
> // This equation is only true if you ignore ordering
> p flatMap { a => f(a) ++ g(a) } = (p flatMap f) ++ (p flatMap g)
>
> p flatMap { a => Seq(a) } = p
>
> p flatMap f flatMap g = p flatMap { a => f(a) flatMap g }
>
>
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/twitter/scalding/pull/1111/files#r21358370>.
>



-- 
Oscar Boykin :: @posco :: http://twitter.com/posco