[Tex/LaTex] \newcommand and comma separated parameters

comma-separated listmacros

I would like to learn to manipulate comma separated lists in Latex.
To give a concreet but artificial example, I would like to have this command:

\swap{1,10}

expand to this:

{10,1}

How can I achieve it?

Best Answer

I think you should ask what you want in full generality. For your concrete example,

\newcommand*\swap[1]{\doswap#1\relax}
\def\doswap#1,#2\relax{{#2,#1}}

should work, although I didn't test it.

Related Solutions

[Tex/LaTex] Comma-separated list

Here some macro which reads the lines as macro arguments. It got inspired by this question. It would be possible to change the "interface" to LaTeX environments instead, but the TeX syntax (without \begin and \end) is easier.

\documentclass{article}

\makeatletter
\newcommand*\commasep[2][, ]{%
   \begingroup
   \def\commasepsep{#1\space}%  store separator e.g. ','
   \def\commasependsep{#2\space}%  store last separator e.g. 'and'
   \@commasep
}
\newcommand*\@commasep[1][.]{%
   \def\commasepend{#1}%  store end marker e.g. '.'
   \@ifnextchar\endcommasep{}{%  check for empty list
     \catcode\endlinechar\active%  make end-of-line active
     \commasepfirstelement%  read first element
   }%
}%
\begingroup
\catcode\endlinechar\active%
% The `~` character represents the end-of-line character in the
% code below:
\lccode`\~=\endlinechar%
\lowercase{%
% Read first element
\gdef\commasepfirstelement#1~}{%
    #1%
    \@ifnextchar\endcommasep{%
      \commasepend% remove this if you don't want one with only one element
    }{%
      \commasepelement% no comma here!
    }%
}%
\lowercase{%
\endgroup%
% Read all other elements
\gdef\commasepelement#1~}{%
    \@ifnextchar\endcommasep{% Stop at `\endcommasep`
      \commasependsep#1\commasepend%
    }{%
      \commasepsep#1\commasepelement%
    }%
}%
\def\endcommasep{%
  \@gobble{endcommasep}% be unique (for `\@ifnextchar`) 
  \endgroup
}%
\makeatother

\begin{document}

% Usage: \commasep[<separator>]{<last separator>}[<end marker>]
xxx\commasep[,]{and}[.]
a
b
c
d
\endcommasep yyy

xxx\commasep{and}
a
\endcommasep yyy

xxx\commasep{and}
\endcommasep yyy

xxx\commasep{or}
a
b
\endcommasep yyy

\end{document}

Please also note that there is a parselines package which might be used. However, it doesn't support handling the last entry different. Nevertheless, its code might be a good read for people interested in this kind of parsing.

[Tex/LaTex] Comma in macro parameters

Well I guess that was a trivial question...

The answer is:

[arg1={a,b},arg2=c]

@Qrrbrbirlbel: thanks.

Best Answer

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[Tex/LaTex] Comma-separated list

[Tex/LaTex] Comma in macro parameters

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