Use roman numerals for cite in BibLaTeX

Question

I'm using BibLaTeX for my bibliography, with the the following options:

\usepackage[backend=bibtex8, citestyle=numeric, defernumbers=true, bibstyle=numeric, autocite=superscript]{biblatex}

I would like to know how I could use roman numerals instead of arabic numerals for enumerating bibliography entries. I have already found that question, but the answer doesn't entirely suit my needs.

What I want is something like this:

Some text. [I]

Bibliography

[I] The corresponding reference.

Instead of this:

Some text. [1]

Bibliography

[1] The corresponding reference.

Thanks in advance!

Answer 1

It should be enough to have

\DeclareFieldFormat{labelnumber}{\Rn{#1}}

for lowercase numerals, or

\DeclareFieldFormat{labelnumber}{\RN{#1}}

for uppercase numerals.

If a shorthand is present it is used instead of a number, but still the labelnumber format seems to apply, so something like

\DeclareFieldFormat{labelnumber}{\ifinteger{#1}{\RN{#1}}{#1}}

is a bit safer.

MWE

\documentclass[ngerman]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[style=numeric,backend=biber]{biblatex}

\DeclareFieldFormat{labelnumber}{\RN{#1}}

\addbibresource{biblatex-examples.bib}
\begin{document}
\cite{sigfridsson,geer,wilde,worman,knuth:ct:a}

\printbibliography
\end{document}

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Since biblatex version 3.1 and more specifically commit e5c2826 the fix previously contained in this answer is obsolete; it has been removed (but can be of course be found in the revision history).