Missing \endcsname inserted in table contents defined within a foreach loop

Question

! Missing \endcsname inserted. \countuno l.67 }

From what I've seen about this error the fact that it is a tex error makes it very difficult to pinpoint its origins. Hopefully this is not the case here but I've personally been unable to find the issue with this document. I have a similar document differing only slightly in that the tabular environment is enclosed by a subtable and the control structures take a different shape. I have a feeling that it might have something to do with the counters used to do some calculations, but I haven't seen anything off with them.

In my document I loop through a master data file and typeset it into a tabular environment by looping through the data file, calculating row placements with counter arithmetic, and bundling all the contents in a \tablecontents macro to be delivered to the tabular environment and expanded.

\documentclass{article}
\usepackage{pgfplots, pgfplotstable}
\usepackage{filecontents}
\usepackage{indentfirst}
\usepackage{amsmath}
\usepackage{float}
\usepackage{hhline}
\usepackage{booktabs}
\usepackage[strict]{changepage}
\usepackage[position=top]{subfig}

\renewcommand\thesection{}
\makeatletter
\renewcommand\thesubsection{\@arabic\c@subsection}
\makeatother

\begin{filecontents}{data.dat}
28.1 0.7 0.9 1.2 1.4 1.5
40.0 11.2 11.7 12.0 12.2 12.9
44.7 18.2 19.3 19.7 19.8 20.4
50.9 28.0 28.9 29.4 29.6 30.1
57.0 43.2 42.2 41.6 40.7 40.4
61.5 50.2 51.0 52.1 52.6 52.7
67.0 62.8 64.5 65.5 65.6 68.5
72.2 78.3 79.2 80.7 80.8 82.7
\end{filecontents}

\pgfplotsset{compat=1.14}
\pgfplotstableread{data.dat}\Data

\begin{document}
\newcount\countuno
\newcount\countdos

\begin{table}[H]
\begin{tabular}{lll}
\toprule
$D$ & $h$ & $h/D$\\
\midrule
\gdef\tablecontents{}%
\foreach\row in {0,...,34}
{%
        \countdos = \row
        \countuno = \row
        \divide\countuno by 5
        \divide\countdos by 5
        \multiply\countuno by -5
        \advance\countuno by \row
        \pgfplotstablegetelem{\countdos}{0}\of\Data\pgfmathsetmacro\elemtable{\pgfplotsretval}%
        \ifnum\countuno=1
                \xdef\tablecontents{%
                        \unexpanded\expandafter{\tablecontents}%
                        \noexpand\pgfmathprintnumber{\elemtable}%
                }%
        \fi
        \pgfplotstablegetelem{\countdos}{\countuno}\of\Data\pgfmathsetmacro\elemtabledos{\pgfplotsretval}%
        \pgfmathsetmacro\elemtabletres{\elemtabledos / \elemtable}
        \xdef\tablecontents{%
                \unexpanded\expandafter{\tablecontents}%
                & \noexpand\pgfmathprintnumber{\elemtabledos} & \noexpand\pgfmathprintnumber{\elemtabletres}\noexpand\\
        }%
        \ifnum\countuno=5 \xdef\tablecontents{%
                        \unexpanded\expandafter{\tablecontents}%
                        \noexpand\midrule\noexpand\\
                }%
        \fi
}
\tablecontents
\bottomrule
\end{tabular}
\end{table}

\end{document}

EDIT: I've done some messing around, and I created a similar chunk of code to take the place of the table in the above and the error is still present, so it is not coming from the tabular environment. When I comment out all references to pointers the error goes away. When scrolling through future error messages the next error---occurring on the same line---is "! Missing number, treated as zero." and the next---also on the same line---is "! Extra \endcsname."

I also tried placing the code \countuno 1 \foreach\row in {0,...,5}{\multiply\countuno\row} \the\countuno before the table and it does not trigger an error so I'm not sure it is the counter arithmetic that is causing the error.

Answer 1

This is presumably a bit closer to what you want. The key change is to use the syntax from p. 61 of the manual, which specifies that [index] must precede a column specification which uses an index rather than a name.

Also, \countuno was never equal to 5 in the original code, so that part of the conditional was never executed. I'm guessing that you want 6 rather than 5 in the earlier definitions, but I'm not certain what the intention is exactly, so I might be mistaken about this.

The reason for the weird placement of the first value is just the effect of all the spaces accumulating in the first cell, which also makes it very wide.

\begin{filecontents}{\jobname.dat}
28.1 0.7 0.9 1.2 1.4 1.5
40.0 11.2 11.7 12.0 12.2 12.9
44.7 18.2 19.3 19.7 19.8 20.4
50.9 28.0 28.9 29.4 29.6 30.1
57.0 43.2 42.2 41.6 40.7 40.4
61.5 50.2 51.0 52.1 52.6 52.7
67.0 62.8 64.5 65.5 65.6 68.5
72.2 78.3 79.2 80.7 80.8 82.7
\end{filecontents}
\documentclass{article}
\usepackage{pgfplots,pgfplotstable}
\usepackage{booktabs}

\pgfplotsset{compat=1.15}
\pgfplotstableread{\jobname.dat}\Data

\begin{document}
\newcount\countuno
\newcount\countdos
\def\tablecontents{}%
\begin{tabular}{lll}
\toprule
$D$ & $h$ & $h/D$\\
\midrule
\foreach\rowx [count=\rh] in {0,...,47}
{%
  \countdos = \rowx
  \countuno = \rowx
  \divide\countuno by 6
  \divide\countdos by 6
  \multiply\countuno by -6
  \advance\countuno by \rowx
  \pgfplotstablegetelem{\countdos}{[index]0}\of\Data
  \pgfmathsetmacro\elemtable{\pgfplotsretval}%
  \ifnum\countuno=0
    \ifnum\rh=1\relax\else
      \xdef\tablecontents{%
        \unexpanded\expandafter{\tablecontents}%
        \noexpand\midrule
      }%
    \fi
    \xdef\tablecontents{%
      \unexpanded\expandafter{\tablecontents}%
      \noexpand\pgfmathprintnumber{\elemtable}%
    }%
  \else
    \pgfplotstablegetelem{\countdos}{[index]\countuno}\of\Data
    \pgfmathsetmacro\elemtabledos{\pgfplotsretval}%
    \pgfmathsetmacro\elemtabletres{\elemtabledos / \elemtable}%
    \xdef\tablecontents{%
      \unexpanded\expandafter{\tablecontents}%
      & \noexpand\pgfmathprintnumber{\elemtabledos} & \noexpand\pgfmathprintnumber{\elemtabletres}\noexpand\\%
    }%
    \ifnum\countuno=5 \xdef\tablecontents{%
        \unexpanded\expandafter{\tablecontents}%
      }%
    \fi
  \fi
}%
\tablecontents
\bottomrule
\end{tabular}

\end{document}