Remove math from command parameter to get only the letters

Question

I use a little command, which prints new defined terms in bold, adds a label and adds them to the index.

\newcommand*{\defined}[1]{{\bf #1}\label{#1}\index{#1}}

Now if I do \defined{$G$-invariant} the label isn't working and the index entry is ordered in the wrong place. I think that's got to do with the math dollar sign. Is there a way to strip this and get for label and index just the G?

Answer 1

Here's how I'd fix it: add a second, optional parameter as the sort key and label:

\documentclass{article}
\usepackage{makeidx}
\usepackage{xparse}
\NewDocumentCommand{\defined}{mg}{%
    {\bfseries #1}%
    \IfNoValueTF{#2}
        {\index{#1}\label{#1}}
        {\index{#2@#1}\label{#2}}
    }
\makeindex
\begin{document}
\defined{$G$-invariant}    % Probably does it wrong

\defined{$G$-invariant}{G-invariant}
\printindex
\end{document}

As an alternative, in accordance with @egreg's suggestion, using the 'Traditional' way of doing optional arguments:

\documentclass{article}
\usepackage{makeidx}
\usepackage{xparse}
\NewDocumentCommand{\defined}{om}{%
    {\bfseries #2}%
    \IfNoValueTF{#1}
        {\index{#2}\label{#2}}
        {\index{#1@#2}\label{#1@#2}}
    }
\makeindex
\begin{document}
\defined{$G$-invariant}

\defined[G-invariant]{$G$-invariant}
\printindex
\end{document}

Answer 2

I'd definitely go with Bianca Lobo's solution (the alternative one, really). But, just for fun, here's another way.

It's possible to strip $ symbols, but this is not the only problem: if you strip $ from \defined{$\Gamma$-function} you'll get into troubles. Moreover, simply stripping the $ would leave incorrect entries in the index in any case.

However one can use the @ feature of \index: with

\index{something@something else}

MakeIndex will use something for the sorting, while writing "something else" as the index entry.

Here's a complicated way to do what you want:

\documentclass{article}
\usepackage{xparse,l3regex}
\usepackage{imakeidx}
\makeindex

\ExplSyntaxOn
\NewDocumentCommand{\defined}{om}
 {
  \textbf{#2}
  \IfNoValueTF{#1}
   % No optional argument: do the complicated test
   { \heinz_index:n {#2} }
   % Optional argument: use the simplest way
   { \label{#1}\index{#1@#2} }
 }
\tl_new:N \l__heinz_index_tl
\cs_new_protected:Npn \heinz_index:n #1
 {
  % test if a $ is present in the argument
  \tl_if_in:nnTF { #1 } { $ }
   { \__heinz_strip:n { #1 } } % a $ is scanned
   { \index{#1} }              % no $, simple case
 }

\cs_new_protected:Npn \__heinz_strip:n #1
 {
  % stringify the argument
  \tl_set:Nx \l__heinz_index_tl { \tl_to_str:n { #1 } }
  % remove $, backslash, spaces
  \regex_replace_all:nnN { ( \$ | \\ | \s ) } { } \l__heinz_index_tl
  % produce the \index command and the label
  \__heinz_do_double_index:nV { #1 } \l__heinz_index_tl
 }
\cs_new_protected:Npn \__heinz_do_double_index:nn #1 #2
 {
  \exp_args:NV \label \l__heinz_index_tl
  \index{#2@#1}
 }
\cs_generate_variant:Nn \__heinz_do_double_index:nn { nV }
\ExplSyntaxOff

\begin{document}
\defined{face}

\defined{$G$-invariant}

\defined{group}

\defined{$\Gamma$-function}

\defined[C-transform]{$\mathcal{C}$-transform}

\pageref{G-invariant}

\clearpage

\printindex

\end{document}

However, in some cases you'll have to express it in the form

\defined[<sorting key>]{<argument>}

as the stripping performed in the case of $\mathcal{C}$-transform will do no good. One might add to the list of tokens to be stripped off, but this is error prone and it doesn't seem really a sensible thing to do.

Note also that you have to use the "stripped" version in \pageref, so do \pageref{G-invariant} and not \pageref{$G$-invariant}. In any case a label such as $\Gamma$-function would be illegal.

Answer 3

Using the etex \scantokens you can locally set $ to be ignored. This removes it from the label key and also from the sort key used by makeindex. The original math string is used after the @ field so it is typeset in the index.

\documentclass{article}
\usepackage{makeidx}


\newcommand*{\defined}[1]{%
{\catcode`\$=9
\scantokens{\gdef\tmp{#1}}}%
\textbf{#1}\label{\tmp}\index{\tmp@#1}}

\makeindex
\begin{document}


\defined{$G$-invariant}

\defined{foo-invariant}


\printindex
\end{document}