How to sort entries of numerically referenced and split bibliographies alphabetically, but having citation numbers in order of appearance?

Question

I've got a question regarding Biblatex with Biber backend. I'd like to have a split bibliography: One for print media and one for online resources. I would like to have quite a special kind of sorting:

• Split bibliographies are done by using keywords.
• The numeric style is used for citations and for bibliography.
• It is necessary that both bibliographies, the one for print media and the one for online media, are sorted alphabetically (e.g. name of authors, year and title).
• The numbers used for the citation labels in the two bibliographies should belong to separate and independent number ranges.
• The citation numbers should be assigned in order of appearance in the text.

I've got a minimum working example:

\documentclass[12pt,oneside]{IEEEtran}
\usepackage[utf8]{inputenc}
\usepackage[%
    backend=biber, 
    defernumbers=true,
    style=numeric,
    sortcites=true,
    sorting=none
]{biblatex}   

\begin{filecontents}{testlit.bib}   
    @BOOK{al2013,
        author =   {Alice},
        title =    {Book of Alice},
        date =     {2013}
    }
    @BOOK{bo2014,
        author =   {Bob},
        title =    {Book of Bob},
        date =     {2014}
    }   
    @ONLINE{to2012,
        keywords = {secondary},
        author =  {Tom},
        title =   {Website of Tom},
        year =    {2012}
    }
    @ONLINE{ja2014,
        keywords = {secondary},
        author =  {James},
        title =   {Website of James},
        year =    {2014}
    }   
\end{filecontents}

\addbibresource{testlit.bib}

\begin{document}
  This is the first book I reference \cite{bo2014}. I can also reference 
  a first online resource \cite{to2012}. At the end of this sentence, I 
  reference the second book \cite{al2013} and the second online resource 
  \cite{ja2014}.

  \printbibliography[%
      notkeyword=secondary,
      heading=subbibliography,
      title={Print Media},
      sorting=nty,
      prefixnumbers={A-}
  ]

  \printbibliography[%
      keyword=secondary,
      heading=subbibliography,
      title={Online Media},
      sorting=nty,
      prefixnumbers={B-}
   ]    
\end{document}

The result I get looks as expected but not as desired:

The problem is that sorting the entries in the two bibliographies results in having the citation numbers in the text in an unsorted way.

If I set defernumbers to false, I get the following result:

This is quite close to the result that I'd like to have. But now both bibliographies share the same number range: There are, for example, no citations with labels A-2 and no B-1.

So my question is: Is there any way to tweak Biblatex and/or Biber to produce something like this:

Of course, it would be even nicer to have suffixes instead of the prefixnumbers, but I could live with that (I have a hack which produces suffixes for the two bibliographies, but it also needs defernumbers to be enabled to function).

Thank you very much in advance!

Kinds regards,

Steffen

Answer 1

It can be done removing sorting=none option when loading biblatex and adding the following lines in your preamble (see https://tex.stackexchange.com/a/37850/27635 for reference):

\AtDataInput{%
  \csnumgdef{entrycount:\strfield{prefixnumber}}{%
    \csuse{entrycount:\strfield{prefixnumber}}+1}}

\DeclareFieldFormat{labelnumber}{\mkbibdesc{#1}}
\newrobustcmd*{\mkbibdesc}[1]{%
  \number\numexpr\csuse{entrycount:\strfield{prefixnumber}}+1-#1\relax}

MWE

\documentclass[12pt,oneside]{IEEEtran}
\usepackage[utf8]{inputenc}
\usepackage[%
    backend=biber,
    defernumbers=true,
    style=numeric,
    sortcites=true,
]{biblatex}

\AtDataInput{%
  \csnumgdef{entrycount:\strfield{prefixnumber}}{%
    \csuse{entrycount:\strfield{prefixnumber}}+1}}

\DeclareFieldFormat{labelnumber}{\mkbibdesc{#1}}
\newrobustcmd*{\mkbibdesc}[1]{%
  \number\numexpr\csuse{entrycount:\strfield{prefixnumber}}+1-#1\relax}

\begin{filecontents}{testlit.bib}
    @BOOK{al2013,
        author =   {Alice},
        title =    {Book of Alice},
        date =     {2013}
    }
    @BOOK{bo2014,
        author =   {Bob},
        title =    {Book of Bob},
        date =     {2014}
    }
    @ONLINE{to2012,
        keywords = {secondary},
        author =  {Tom},
        title =   {Website of Tom},
        year =    {2012}
    }
    @ONLINE{ja2014,
        keywords = {secondary},
        author =  {James},
        title =   {Website of James},
        year =    {2014}
    }
\end{filecontents}

\addbibresource{testlit.bib}

\begin{document}
  This is the first book I reference \cite{bo2014}. I can also reference
  a first online resource \cite{to2012}. At the end of this sentence, I
  reference the second book \cite{al2013} and the second online resource
  \cite{ja2014}.

  \printbibliography[%
      notkeyword=secondary,
      heading=subbibliography,
      title={Print Media},
      sorting=nty,
      prefixnumbers={A-}
  ]

  \printbibliography[%
      keyword=secondary,
      heading=subbibliography,
      title={Online Media},
      sorting=nty,
      prefixnumbers={B-}
   ]
\end{document} 

Output