Different sorting schemes for different entry types?

Question

I'm writing my own style and for most entry types the type field must be printed after the title, but for some entries it must be printed before. So for some entry types I need the type field to be sorted before the title field, and for some I need it to be sorted after. Is there a way to do that?

---

MWE

\begin{filecontents}{\jobname.bib}
@book{abook,
    author = {Alfred A.},
    title = {A Book},
    type = {B Type}}
@book{anotherbook,
    author = {Alfred A.},
    title = {Another Book},
    type = {A Type}}
@article{anarticle,
    author = {Alfred A.},
    title = {An Article},
    type = {C Type}}
\end{filecontents}

\documentclass{article}

\usepackage[backend=biber, bibstyle=standard]{biblatex}
\addbibresource{\jobname.bib}

\DeclareBibliographyDriver{book}{
    \printnames{author}
    \newunit
    \printfield{title}
    \newunit
    \printfield{type}
}

\DeclareBibliographyDriver{article}{
    \printnames{author}
    \newunit
    \printfield{type}
    \newunit
    \printfield{title}
}

\DeclareSortingScheme{nty}{
  \sort{
    \field{presort}
  }
  \sort[final]{
    \field{sortkey}
  }
  \sort{
    \field{sortname}
    \field{author}
    \field{editor}
    \field{sorttitle}
    \field{title}
    \field{subtitle}
  }
  \sort{
    %\field{type}
    \field{sorttitle}
    \field{title}
    \field{subtitle}
  }
  \sort{
    \field{sortyear}
    \field{year}
  }
  \sort{
    \field[padside=left,padwidth=4,padchar=0]{volume}
    \literal{0000}
  }
}

\begin{document}
  \nocite{*}
  \printbibliography
\end{document}

This is what I get:

Since it's sorted by title before type, "An Article" comes before "Another Book", when it should actually come last, since it's type starts with a "C".

Now if I uncomment that row that says \field{type} I get this:

Since it's sorted by type before title, "Another Book" comes before "A Book", when the opposite should be true.

---

This answer suggests using the sortkey field, but in my case this won't work, since the author always comes first.

Answer 1

It's an odd requirement since you will have to mirror the formatting somehow before the sorting happens. You could do it with sourcemaps by appending things to a custom field in the right order. Here is something to get you going which makes your MWE work:

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \pertype{book}
      \step[fieldsource=title]
      \step[fieldset=usera, origfieldval]
      \step[fieldsource=type]
      \step[fieldset=usera, origfieldval, append]
    }
    \map{
      \pertype{article}
      \step[fieldsource=type]
      \step[fieldset=usera, origfieldval]
      \step[fieldsource=title]
      \step[fieldset=usera, origfieldval, append]
    }
  }
}

Then your sorting would be:

\DeclareSortingScheme{nty}{
  \sort{
    \field{presort}
  }
  \sort[final]{
    \field{sortkey}
  }
  \sort{
    \field{sortname}
    \field{author}
    \field{editor}
    \field{sorttitle}
    \field{title}
    \field{subtitle}
  }
  \sort{
    \field{usera}
  }
  \sort{
    \field{sortyear}
    \field{year}
  }
  \sort{
    \field[padside=left,padwidth=4,padchar=0]{volume}
    \literal{0000}
  }
}

Although it's not really nty sorting any more and you should probably name it something else.