\citenum with square brackets

Question

I am using the superscript citation style and sometimes in the text I need to print the citation number is square brackets like [6]. I read I could use \citenum but [\citenum{myref}] leaves some big space before the number [ 6]. Is there anyway I can achive this nicely?

EDIT. These are my natbib options:

 \usepackage[square, comma, sort&compress,authoryear]{natbib}
 \bibpunct{[}{]}{,}{s}{}{;}

Answer 1

The following attempt (a redefinition of \citenum) removes most (?) of the spacing. Sorry for not providing a real solution, but the natbib internals are nothing one wants to delve into.

\documentclass{article}

\usepackage[square,comma,sort&compress,authoryear]{natbib}
\bibpunct{[}{]}{,}{s}{}{;}

\makeatletter
\DeclareRobustCommand\citenum
   {\begingroup
%      \NAT@swatrue\let\NAT@ctype\z@\NAT@parfalse\let\textsuperscript\NAT@spacechar% DELETED
     \NAT@swatrue\let\NAT@ctype\z@\NAT@parfalse\let\textsuperscript\relax% NEW
     \NAT@citexnum[][]}
\makeatother

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@misc{A01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
}
\end{filecontents}

\begin{document}

Some text \citep{A01}.

[\citenum{A01}]

\bibliographystyle{plainnat}
\bibliography{\jobname}

\end{document}

Answer 2

I found that inserting a couple of negative spaces (\!) works fine. e.g.

These are outlined in an excellent review by Foo [\!\!\citenum{Foo2012}]; however, we choose to...

Perhaps this is not a very elegant solution in terms of understanding the problem, but it is concise!