Combine siunitx S column with input value from tex file

Question

I would like to write small tex files containing values with an external program and then show the result in my main tex file using \input in an siunitx S column.

Lets assume a file named pi_file.tex with the content 3.141592654 exists in the current folder.

The minimal (non-working) example is as follows:

\documentclass{article}
\usepackage{siunitx}
\usepackage{xcolor}

\begin{document}
\begin{table} \centering
    \caption{Table with \texttt{S} column type.}
    \begin{tabular}{cS}
        \hline
        Symbol & {Value} \\
        \hline
        $\pi$ & \input{pi_file.tex} \\
        Red $\pi$ & \color{red} 6.283185307 \\
        \hline
    \end{tabular}
\end{table}
\end{document}

I think, the macro expansion for \input takes place later than the work needed for siunitx S column formatting. How can I still use my external file pi_file.tex with siunitx S columns?

The result should of course look like this:

Based on a comment, I managed to load a value in the table, but I am not able to make it a new command which takes the filename as an argument:

\documentclass{article}
\usepackage{siunitx}
\usepackage{xcolor}

\def\inputval{0}
\newread\inputFile
\openin\inputFile=pi_file.tex
\read\inputFile to \inputval
\closein\inputFile

\begin{document}
\begin{table} \centering
    \caption{Table with \texttt{S} column type.}
    \begin{tabular}{cS}
        \hline
        Symbol & {Value} \\
        \hline
        $\pi$ & \inputval \\
        Red $\pi$ & \color{red} 283186.12 \\
        \hline
    \end{tabular}
\end{table}
\end{document}

Answer 1

You need an expandable version of \input; the standard one in LaTeX isn't, the TeX primitive \@@input is.

Here I use filecontents just to make the example self-contained (and to not clobber my files).

\begin{filecontents*}{\jobname-pi.tex}
3.141592654
\end{filecontents*}

\documentclass{article}
\usepackage{siunitx}
\usepackage{xcolor}
\usepackage{booktabs}

\makeatletter
\newcommand{\expinput}[1]{\@@input #1}
\makeatother

\begin{document}

\begin{table}
\centering
\caption{Table with \texttt{S} column type.}

\begin{tabular}{cS[table-format=1.9]}
\toprule
Symbol & {Value} \\
\midrule
$\pi$ & \expinput{\jobname-pi.tex} \\
Red $\pi$ & \color{red} 6.283185307 \\
\bottomrule
\end{tabular}

\end{table}

\end{document}

Answer 2

like this?

i'm not sure if i correctly understood your question. anyway, above table is generated by:

\documentclass[margin=3mm,preview]{standalone}
\usepackage{siunitx}
\usepackage{xcolor}

\def\inputval{0}
\newread\inputFile
\openin\inputFile=pi_file.tex
\read\inputFile to \inputval
\closein\inputFile

\usepackage{etoolbox}% <-- new
\newcommand{\sred}{\color{red}} % renew def. for colored font
\robustify\sred

\begin{document}
    \begin{table}
\centering
    \caption{Table with \texttt{S} column type.}
\begin{tabular}{cS[table-format=1.9]}
        \hline
Symbol          & {Value} \\
        \hline
$\pi$           & \inputval \\
Red $\pi$       & \sred 3.141 592 653 \\
        \hline
\end{tabular}
    \end{table}
\end{document}

Answer 3

This may helps to do what you want:

\documentclass{article}
\usepackage{siunitx}
\usepackage{xcolor}
\usepackage{pgffor}
\usepackage{filecontents}

\begin{filecontents*}{InpFile1.tex}
3.1   
\end{filecontents*}
\begin{filecontents*}{InpFile2.tex}
3.14   
\end{filecontents*}
\begin{filecontents*}{InpFile3.tex}
13.1415   
\end{filecontents*}

\newcounter{myInputCounter}

\newcommand{\myinputcomand}[2]{
\def\inputval{0}
\newread\inputFile
\openin\inputFile=#1\themyInputCounter.tex
\read\inputFile to \inval
\closein\inputFile
\global\expandafter\let\csname #2\themyInputCounter\endcsname\inval
}

%Arguments for ReadNEnumInputFromEnumFiles command:
%1. The number of files (and values) that will be used
%2. The basic name of the files (without the following enumeration and the `.tex` extension)
%3. The basic name of the values (without their enumeration).
\newcommand{\ReadNEnumInputFromEnumFiles}[3]{
\setcounter{myInputCounter}{0}
\foreach \i in {1,...,#1}{\stepcounter{myInputCounter}\myinputcomand{#2}{#3}}
}

\begin{document}
\ReadNEnumInputFromEnumFiles{3}{InpFile}{InVal}
\begin{table} \centering
    \caption{Table with \texttt{S} column type.}
    \begin{tabular}{cS}
        \hline
        Symbol & {Value} \\
        \hline
        Red $\pi$ & \color{red} 13.12 \\
        next enumerated &\\
        no 1 & \csname InVal1\endcsname\\
        no 2 & \csname InVal2\endcsname\\
        no 3 & \csname InVal3\endcsname\\
        \hline
    \end{tabular}
\end{table}
\end{document}

You have to give the command \ReadNEnumInputFromEnumFiles before the table.

with arguments:

1. The number of files (and values) that will be used
2. The basic name of the files (without the following enumeration and the .tex extension)
3. The basic name of the values (without their enumeration).

Then in the table you have to use the values inside \csname (As you named them in the second argument of previous command and with their number in the end)

Output: