Select largest value from a list of variables in LaTeX

Question

I am trying to adapt this example How to iterate over a comma separated list? as my base. Except, rather than display all values, I actually want to iterate through all the values and only return / display the largest one.

The list of numbers I actually want to pass to a custom function will actually be glossaries labels. I have tested it and I can insert \gls{label} into a command like \clist_map_inline:nn { #1 } {\glsentryname{##1} } This works right away to display a list of my expanded values (which are actually numbers) so I am not worried about this part.

I haven't been able to figure out yet:

1. How can I stop this function from typsetting the text, but rather allow me to iterate through the list update a variable only displaying the final value?

   • For example at the start of the loop I would set a dummy value such as -100000
   • and the comparison would compare ##1 iteratively with the dummy variable.
   • With a function call such as a call to my macro \pickGE included below I would then return and update the value if the value in the list is greater than the dummy.

2. What approach would be appropriate to setup a dummmy variable that can be updated in this context

3. How would I finally report this final selected value.
   • I would like to wrap this final value in a \num[scientific-notation = fixed, fixed-exponent = 0, group-digits=false]{} call.

The complete MWE I want to insert

\documentclass{article}
\usepackage{fp}
\usepackage{siunitx}
\usepackage{xparse}
\ExplSyntaxOn

\NewDocumentCommand{\findLargest}{ m }
 {
  \begin{enumerate}
  \clist_map_inline:nn { #1 } { \item \fbox{##1} }
  \end{enumerate}
 }

\ExplSyntaxOff

\newcommand{\pickGE}[2]{%
    \ifboolexpr{test {\ifdimgreater{{#1} pt}{{#2} pt}}}%
    {%
        \FPeval{result}{{#1}}%
    }% true
    {%
        \FPeval{result}{{#2}}%
    }% false
}


\begin{document}

\findLargest{1, 2 ,3 6, 3,1}

\end{document}

Limitations

• I am committed to using XeLaTeX
• I may be misremembering but I also have a vague recollection that siunitx had something to do this directly...
• I am happy to use any other package or approach much like the one employed here (that I wasn't able to make work with my glossaries labels Iterating through comma-separated arguments
• I am not limited to only comma separated lists but based on the shear volume of questions this looked like a good way to go.

Answer 1

Use the max function provided by expl3 in the fp module:

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn

\NewDocumentCommand{\findLargest}{ om }
 {
  \IfNoValueTF{#1}
   {% separator is a comma, directly use \fp_eval:n { max ( #2 ) }
    \engbird_compute_max:n { #2 }
   }
   {% we need to pass the separator
    \engbird_find_largest:nn { #1 } { #2 }
   }
 }

\seq_new:N \l_engbird_largest_seq
\tl_new:N \l_engbird_largest_tl

\cs_new_protected:Npn \engbird_find_largest:nn #1 #2
 {
  % split the input at the stated separator
  \seq_set_split:Nnn \l_engbird_largest_seq { #1 } { #2 }
  % build a comma separated list
  \tl_set:Nx \l_engbird_largest_tl { \seq_use:Nn \l_engbird_largest_seq {,} }
  % compute the max
  \engbird_compute_max:V \l_engbird_largest_tl
 }
% syntactic sugar
\cs_new:Npn \engbird_compute_max:n #1
 {
  \fp_eval:n { max (#1) }
 }
\cs_generate_variant:Nn \engbird_compute_max:n { V }

\ExplSyntaxOff

\begin{document}

\findLargest{1, 2 ,3, 6, 3,1}

\findLargest[;]{ 1.5 ; sqrt(2) ; pi/2 }

\end{document}

If you want to use \num and you don't need different separators, here's a way, that also allows to override the options passed by default to \num:

\documentclass{article}
\usepackage{xparse}
\usepackage{siunitx}
\ExplSyntaxOn

\NewDocumentCommand{\findLargest}{ O{}m }
 {
  \num[
    scientific-notation = fixed,
    fixed-exponent = 0,
    group-digits=false,
    #1
  ] { \engbird_compute_max:n { #2 } }
 }

\cs_new:Npn \engbird_find_largest:nn #1 #2
 {
  \engbird_compute_max:V \l_engbird_largest_tl
 }
% syntactic sugar
\cs_new:Npn \engbird_compute_max:n #1
 {
  \fp_eval:n { max (#1) }
 }
\cs_generate_variant:Nn \engbird_compute_max:n { V }

\ExplSyntaxOff

\begin{document}

\findLargest{1, 2 ,3, 6, 3,1}

\findLargest[group-digits=true]{10000,20000}

\findLargest[round-mode=places]{ 1.5, sqrt(2), pi/2 }

\end{document}