Add created parameters in child file to main.tex

Question

My code/idea from 2 topics: Input a parameter from another file filecontents: select rows of group to display

File parameters.tex:

\documentclass{article}
\usepackage[utf8]{vietnam}
\usepackage{verbatim}
\usepackage{comment}
\usepackage{filecontents}
\begin{filecontents*}{products.tex}
No|Time|Velocity
11|"5s"|"3m/s"
22|"10s"|"7m/s"
33|"20s"|"14m/s"
\end{filecontents*}
\usepackage{datatool}
\DTLsetseparator{|}
\DTLloaddb[autokeys=false]{products}{products.tex}
\newcommand{\printtype}[1]{%
  \par
   \DTLforeach*
    [\DTLiseq{\No}{#1}]% Condition
    {products}% Database
    {\No=No,\Time=Time,\Velocity=Velocity}{%
    time = \Time     \par max\_velocity =  \Velocity
    }% 
}

\begin{document}
\printtype{11}
\end{document}

Compiling this parameters.tex file produces a DVI or PDF file containing:

time = 5s
max_velocity = 3m/s

But I would like to parse this output from the following main.tex file and be able to use the “time” and “max_velocity” values from within main.tex.

File main.tex:

\documentclass{article}

\usepackage{xparse}

\ExplSyntaxOn

\ior_new:N \ar_param_file

\seq_new:N \g_ar_param_seq


\cs_new:Nn \ar_read_by_line:n {%
  \seq_gput_right:Nn \g_ar_param_seq {#1}% Appending the current line to the global sequence buffer
}
\NewDocumentCommand{\paraminput}{O{}m}{%
  \seq_gclear:N \g_ar_param_seq% Clearing the sequence
  \ior_open:Nn \ar_param_file {#2} % Open the input file
  \ior_map_inline:Nn \ar_param_file {\ar_read_by_line:n{##1}}% Reading line by line
  \ior_close:N \ar_param_file% Closing the line
  \seq_map_inline:Nn \g_ar_param_seq {% Traversing through the line
    \seq_set_split:Nnn \l_tmpa_seq {=} {##1} % Splitting each line into 'key=value' pairs
    \seq_if_in:NxT \l_tmpa_seq {#1} {\seq_item:Nn \l_tmpa_seq {2}\seq_map_break:}% Checking if `#1` is in the sequence and display it with \seq_item:Nn..., then break the mapping loop.
  }
}

\ExplSyntaxOff

\begin{document}
The trajectory travels the distance of 
\paraminput[time]{parameters.tex}. % <==========================
The maximum observed velocity is \paraminput[max_velocity]{parameters.tex}. ...
\end{document}

I use LaTeX, texmarker? How can I use the parameters output by parameters.tex from within main.tex? Do I need R or only LaTeX?

Answer 1

Apparently, you really want to write to an intermediate file in text format. Here is one way to do that, with \write (note that the output file is named parameters.txt).

Contents of parameters.tex:

\RequirePackage{filecontents}

\begin{filecontents*}{products.tex}
No|Time|Velocity
11|"5s"|"3m/s"
22|"10s"|"7m/s"
33|"20s"|"14m/s"
\end{filecontents*}

\documentclass{article}
\usepackage{datatool}
\DTLsetseparator{|}
\DTLloaddb[autokeys=false]{products}{products.tex}

\newwrite\myOutput
\immediate\openout\myOutput=parameters.txt
\AtEndDocument{\immediate\closeout\myOutput}

\newcommand{\printForNumber}[1]{%
  \DTLforeach*%
    [\DTLiseq{\No}{#1}]% Condition
    {products}% Database
    {\No=No,\Time=Time,\Velocity=Velocity}{%
      \immediate\write\myOutput{time=\Time}%
      \immediate\write\myOutput{max_velocity=\Velocity}%
    }%
  }

\begin{document}
\printForNumber{11}
\end{document}

This produces a file called parameters.txt, containing the following lines:

time=5s
max_velocity=3m/s

Your main.tex code works with that, at the condition that you replace parameters.tex with parameters.txt in the two \paraminput[〈param name〉]{〈file〉} calls. However, the way used in your main.tex code to select the first line containing the desired parameter name (here: time or max_velocity) can be improved a little bit—you'll find my proposal below. The main problem in my opinion is that your equality test for the given parameter name applies to both sides of the equal sign: the parameter name (okay) and also the parameter value (not fantastic...).

I also tried to arrange the code according to LaTeX3-recommended code style (see The LaTeX3 Pro­gram­ming Lan­guage and LaTeX3 style guide on this page). I moved the whole logic of the \paraminput command into a new \ar_find_data_in_file:nn protected command, so that the document-level command (\paraminput) just calls \ar_find_data_in_file:nn with its two arguments. The empty default value for the optional argument of \paraminput is strange, but I suppose you are going to replace it with time, max_velocity or something like that. Therefore, I didn't change this optional argument into a mandatory one. So, here is the revised main.tex file:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\ior_new:N \g_ar_param_file
\seq_new:N \g_ar_param_seq

\cs_new_protected:Nn \__ar_read_by_line:n
  {
    % Append the current line to the global sequence \g_ar_param_seq
    \seq_gput_right:Nn \g_ar_param_seq {#1}
  }

% #1: parameter name such as 'time' or 'max_velocity'
% #2: input file
\cs_new_protected:Npn \ar_find_data_in_file:nn #1#2
  {
    \seq_gclear:N \g_ar_param_seq      % Clear the sequence
    \ior_open:Nn \g_ar_param_file {#2} % Open the input file #2
    % Read it line by line into sequence \g_ar_param_seq
    \ior_map_inline:Nn \g_ar_param_file { \__ar_read_by_line:n {##1} }
    \ior_close:N \g_ar_param_file      % Close the file

    \seq_map_inline:Nn \g_ar_param_seq % For each line
      { % Split it around the '=' sign
        \seq_set_split:Nnn \l_tmpa_seq {=} {##1}
        % Get the parameter name
        \seq_get_left:NN \l_tmpa_seq \l_tmpa_tl

        % If #1 is the name of the parameter for the current line, leave it in
        % the TeX input stream and break out of the mapping loop.
        \str_if_eq:VnT \l_tmpa_tl {#1}
          {
            \seq_map_break:n % Get the parameter value and break
              { \seq_item:Nn \l_tmpa_seq { 2 } }
          }
      }
  }

\NewDocumentCommand \paraminput { O{} m }
  {
    \ar_find_data_in_file:nn {#1} {#2}
  }

\ExplSyntaxOff

\begin{document}
The trajectory took \paraminput[time]{parameters.txt}.
The maximum observed velocity was \paraminput[max_velocity]{parameters.txt}.
\end{document}