How to make a column specifier which combines 'X' and 'S'?

Question

How to use siunitx and tabularx together? works great if you want every X column to be interpreted by siunitx, however, what if I want that for just a few tables? So, is it possible to have the S[opt] column behavior with automatic width?

I'm struggling with the optional arguments part of the S column, so far this is what I've got.

MWE

\documentclass{article}
\usepackage{array,tabularx,siunitx,booktabs}
\usepackage[utf8]{inputenc}

% Allow `_` and `:` in macro names (LaTeX3 style)
\catcode`\_=11
\catcode`\:=11
% Internal code of `S`
\newcolumntype{Y}[1]{% << mandatory argument (how to make it optional?)
    >{\__siunitx_table_collect_begin:Nn S{#1} }%
    X%
    <{\__siunitx_table_print:}%
}
\catcode`\_=8
\catcode`\:=12
\begin{document}

    \begin{table}[h]
        \centering
        \caption{Some table}
        \begin{tabularx}{\textwidth}{Y{}Y{}Y{}}
            \toprule
            {Tempo (min)} & {Fase A (\%v/v)} & {Fase B (\%v/v)} \\ 
            \midrule
               0,01     &       100      &    0\\
                15      &       80       &    20\\
                25      &       80       &    20\\
                30      &       100      &    0\\
            \bottomrule
        \end{tabularx}
    \end{table}

\end{document}

If the answer is "No that's not possible" it's ok, but it would be nice to have it running perfectly. :D

Someone will ask why use tabularx for numeric columns, easy explanation: crazy advisor requirement. If it was up to me... :)

Answer 1

If you really like to have tabularx:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{booktabs,tabularx}
\newcommand\mcx[1]{\multicolumn{1}{>{\centering\arraybackslash}X}{#1}}
\usepackage{siunitx}

\begin{document}

\begin{table}[htp]%never just [h]
    \centering
    \caption{Some table}
    \begin{tabularx}{\textwidth}{*{3}{S[table-format=3.2]}}
        \toprule
    \mcx{Tempo (min)} & \mcx{Fase A (\%v/v)} & \mcx{Fase B (\%v/v)} \\
        \midrule
     0,01   &       100      &    0\\
    15      &       80       &    20\\
    25      &       80       &    20\\
    30      &       100      &    0\\
        \bottomrule
    \end{tabularx}
\end{table}

\end{document}

but result is (to my opinion) far worse than obtained in other answers. It can be slightly improved, if you reduce table width, but why then you make such complication if this can be done automatically without tabularx?

Answer 2

You want tabular*, not tabularx. But the result is wrong anyway, as you can clearly see from the image below.

\documentclass{article}
\usepackage{array,siunitx,booktabs}
\usepackage[utf8]{inputenc}

\begin{document}

\begin{table}[htp]
\centering
\caption{Some table}\label{label}

\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}SSS@{}}
\toprule
{Tempo (\si{min})} & {Fase A ($\%v/v$)} & {Fase B ($\%v/v$)} \\ 
\midrule
 0,01 & 100 &  0\\
15    &  80 & 20\\
25    &  80 & 20\\
30    & 100 &  0\\
\bottomrule
\end{tabular*}

\end{table}

\begin{table}[htp]
\centering
\caption{Some table}\label{label2}

\begin{tabular}{@{}SSS@{}}
\toprule
{Tempo (\si{min})} & {Fase A ($\%v/v$)} & {Fase B ($\%v/v$)} \\ 
\midrule
 0,01 & 100 &  0\\
15    &  80 & 20\\
25    &  80 & 20\\
30    & 100 &  0\\
\bottomrule
\end{tabular}

\end{table}

\end{document}

Answer 3

To spread the columns out to textwidth you want tabular* not tabularx but this should really be a non-aim, as it just makes the table harder to read.

this also makes it easy to use the S optional argument as optional

\documentclass{article}
\usepackage{array,tabularx,siunitx,booktabs}
\usepackage[utf8]{inputenc}

\begin{document}

    \begin{table}[htp]%never just [h]
        \centering
        \caption{Some table}
        \begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}SSS@{}}
            \toprule
            {Tempo (min)} & {Fase A (\%v/v)} & {Fase B (\%v/v)} \\ 
            \midrule
               0,01     &       100      &    0\\
                15      &       80       &    20\\
                25      &       80       &    20\\
                30      &       100      &    0\\
            \bottomrule
        \end{tabular*}
    \end{table}

\end{document}