Customized citation keys with biblatex

Question

I have what follows:

\documentclass{article}
\begin{filecontents*}{mybib.bib}
@ARTICLE{refconf,
    author = {author},
    title = {title},
    keywords = {conference}}
@ARTICLE{refjour,
    author = {author},
    title = {title},
    keywords = {journal}}
@ARTICLE{ref,
    author = {author},
    title = {title}}
\end{filecontents*}
\usepackage[style=numeric-comp,backend=biber]{biblatex}
\bibliography{mybib}
\defbibheading{bibempty}{}

\begin{document}
\cite{refjour}, \cite{refconf}, \cite{ref}
\subsection{Personal Conference references}
\printbibliography[keyword=conference,heading=bibempty]
\subsection{Personal Journal references}
\printbibliography[keyword=journal,heading=bibempty]
\subsection{Other references}
\printbibliography[heading=bibempty]
\end{document}

which is not too bad but I need to customize the labels such that \cite{refjour} yields [j.1] (j. for journal) in the main text as well as in the list of references, and that \cite{refconf} yields [c.1], and finally \cite{ref} yields [1].

Answer 1

A similar question to this one was recently posted. Prefixes to labelnumber can be easily added using the prefixnumbers option of \printbibliography. This option needs defernumbers enabled globally. For the last reference list, you'll probably want to filter out the previous keywords. The notkeyword filter can be used more than once. All this is demonstrated using your MWE below.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[american]{babel}
\usepackage{csquotes}
\usepackage[style=numeric-comp,defernumbers=true]{biblatex}

\begin{filecontents*}{\jobname.bib}
@ARTICLE{refconf,
    author = {author},
    title = {title},
    keywords = {conference}}
@ARTICLE{refjour,
    author = {author},
    title = {title},
    keywords = {journal}}
@ARTICLE{ref,
    author = {author},
    title = {title}}
\end{filecontents*}
\addbibresource{\jobname.bib}

\begin{document}
\cite{refjour}, \cite{refconf}, \cite{ref}
\printbibheading
\printbibliography[keyword=conference,prefixnumbers={c.},
  heading=subbibliography,title={Personal Conference references}]
\printbibliography[keyword=journal,prefixnumbers={j.},
  heading=subbibliography,title={Personal Journal references}]
\printbibliography[notkeyword=journal,notkeyword=conference,prefixnumbers={},
  heading=subbibliography,title={Other references}]
\end{document}