Loading data from csv into arrays [arrayjobx]: problems retrieving values

Question

As a follow-up to several questions, I've come up with the following MWE, with the aim of filling an array (via arrayjobx) with values loaded from a CSV file.

The desired output is to print something like this:

---------------------------------------
|            |   John Doe (084754)    |
|  Students: |  Carl Sagan (458736)   |
|            | Peanut Butter (432756) |
---------------------------------------

The CSV:

Campo,Valor,Aux
alumno,"John Doe","084754"
alumno,"Carl Sagan","458736"
alumno,"Peanut Butter","432576"

The LaTeX document:

\documentclass{minimal}

\usepackage{arrayjobx,datatool,multirow,forloop}

\newcounter{numst}

% Offending line vvv
\newcommand{\addstudent}[2]{\expandafter\addstudentaux\expandafter{#1}\expandafter{#2}}

\newcommand{\addstudentaux}[2]{%
    \stepcounter{numst}%
    \ifthenelse{\equal{\value{numst}}{1}}{\newarray\Students\newarray\Boletas}{}
    \Students(\arabic{numst})={#1}%
    \Boletas(\arabic{numst})={#2}%
}

\newcommand{\IsEmptyElement}[2]{\ifthenelse{\boolean{emptydata}}{#1}{#2}}

\AtEndDocument{\ifthenelse{\value{numst} > 0}{\delarray\Students\delarray\Boletas}{}}

\begin{document}
    \DTLloaddb{Datos}{datos.csv}
    \DTLforeach{Datos}{\campo=Campo,\valor=Valor,\valorb=Aux}{%
        \ifthenelse{\equal{\campo}{alumno}}{%
            \addstudent{\valor}{\valorb}
        }{}
    }

    \begin{tabular}{cc}
        \ifthenelse{\value{numst} > 0}{%
            \ifthenelse{\value{numst} = 1}{%
                \textbf{Student:} & \Students(1) \\
                \textbf{ID:} & \Boletas(1) \\
            }{%
                \multirow{\value{numst}}{*}{\textbf{Students:}}%
                \newcounter{st}%
                \forloop{st}{1}{\not{\value{st} > \value{numst}}}{%
                    \checkBoletas(\arabic{st})%
                    & \Students(\arabic{st}) \IsEmptyElement{}{(\Boletas(\arabic{st}))} \\%
                }%
            }
        }{}
    \end{tabular}
\end{document}

Output:

How can I retrieve these values correctly? \expandafter only helps on retrieving, at most, one value successfully. Thanks in advance!

EDIT: I'm doing it this way as there'll be other data appended at the end of the table.

Answer 1

Your use of expansion was passing the wrong items to \addstudentaux. Instead, I've used a \begingroup\edef\x{\endgroup <stuff>}\x trick to expand content in <stuff>:

\documentclass{article}

\usepackage{filecontents}
\begin{filecontents*}{datos.csv}
Campo,Valor,Aux
alumno,"John Doe","084754"
alumno,"Carl Sagan","458736"
alumno,"Peanut Butter","432576"
\end{filecontents*}

\usepackage{arrayjobx,datatool,multirow,forloop}

\newcounter{numst}

\newcommand{\addstudent}[2]{%
    \stepcounter{numst}%
    \ifthenelse{\equal{\value{numst}}{1}}{\newarray\Students\newarray\Boletas}{}
    \Students(\arabic{numst})={#1}%
    \Boletas(\arabic{numst})={#2}%
}

\newcommand{\IsEmptyElement}[2]{\ifthenelse{\boolean{emptydata}}{#1}{#2}}

\AtEndDocument{\ifthenelse{\value{numst} > 0}{\delarray\Students\delarray\Boletas}{}}

\begin{document}
\DTLloaddb{Datos}{datos.csv}
\DTLforeach{Datos}{\campo=Campo,\valor=Valor,\valorb=Aux}{%
  \ifthenelse{\equal{\campo}{alumno}}{%
    \begingroup\edef\x{\endgroup\noexpand\addstudent{\valor}{\valorb}}\x
  }{}
}

\begin{tabular}{cc}
  \ifthenelse{\value{numst} > 0}{%
    \ifthenelse{\value{numst} = 1}{%
      \textbf{Student:} & \Students(1) \\
      \textbf{ID:} & \Boletas(1) \\
    }{%
      \multirow{\value{numst}}{*}{\textbf{Students:}}%
      \newcounter{st}%
      \forloop{st}{1}{\not{\value{st} > \value{numst}}}{%
        \checkBoletas(\arabic{st})%
        & \Students(\arabic{st}) \IsEmptyElement{}{(\Boletas(\arabic{st}))} \\%
      }%
    }
  }{}
\end{tabular}
\end{document}

Without the bigger picture, there's not much one can do in terms of code suggestion and/or improvement(s).

---

Here is just a simple implementation that achieves the same output without using arrayjobx:

\documentclass{article}

\usepackage{filecontents}
\begin{filecontents*}{datos.csv}
Campo,Valor,Aux
alumno,"John Doe","084754"
alumno,"Carl Sagan","458736"
alumno,"Peanut Butter","432576"
\end{filecontents*}

\usepackage{datatool}

\begin{document}
\DTLloaddb{Datos}{datos.csv}

\begin{tabular}{cc}
  \textbf{Students:} &
  \begin{tabular}{@{}c@{}}
    \DTLforeach{Datos}{\campo=Campo,\valor=Valor,\valorb=Aux}{%
      \ifthenelse{\equal{\campo}{alumno}}{%
        \valor~(\valorb) \\
      }{}
    }
    \\[-\normalbaselineskip]
  \end{tabular}
\end{tabular}

\end{document}