[Tex/LaTex] Excluding every nth row in pgfplotstable

pgfplotstable

I need to exclude every 0th, 3rd, 6th … row from a table. \pgfmathparse{Mod(#1, 3) == 0} did not work inside row predicate/.code={}, it gives following error:

! Package PGF Math Error: Sorry, the operation 'Mod' has not yet been implemented in the floating point unit :-( (in 'Mod(0, 3) == 0').

I have copied following MWE from another question. I want to exclude rows according to their indices, not according to their values.

\documentclass{minimal}
\usepackage{pgfplotstable}
\begin{document}
\pgfplotstableread{
  num       value
  1         2
  2         5
  1         3
  3         2
  1         4
  2         1
}\data
\pgfplotstabletypeset[row predicate/.code={%
  \ifnum\pgfplotstablegetelem{#1}{num}\of{\data}=1\relax
  \else\pgfplotstableuserowfalse\fi}]{\data}
\end{document}

Best Answer

If you want to filter every nth row, you can use \pgfmathparse{int(mod(#1,3))} (note the lower case m) and then use \ifnum\pgfmathresult>0\relax to check whether to use the row or not:

\documentclass{article}
\usepackage{pgfplotstable}
\begin{document}
\pgfplotstableread{
  num       value
  1         2
  2         5
  1         3
  3         2
  1         4
  2         1
}\data
\pgfplotstabletypeset[row predicate/.code={%
  \pgfplotstablegetelem{#1}{num}\of{\data}
  \pgfmathparse{int(mod(#1,3))}
  \ifnum\pgfmathresult>0\relax
  \else\pgfplotstableuserowfalse\fi}]{\data}
\end{document}

If you want to filter by the value of a cell, as in your code sample, you'll need to adjust your code slightly:

The \pgfplotstablegetelem macro does not expand to its return value; instead, it writes the return value to a macro called \pgfplotsretval. If you use that macro in the \ifnum condition, it works as expected:

\documentclass{article}
\usepackage{pgfplotstable}
\begin{document}
\pgfplotstableread{
  num       value
  1         2
  2         5
  1         3
  3         2
  1         4
  2         1
}\data
\pgfplotstabletypeset[row predicate/.code={%
  \pgfplotstablegetelem{#1}{num}\of{\data}
  \ifnum\pgfplotsretval=1\relax
  \else\pgfplotstableuserowfalse\fi}]{\data}
\end{document}
Related Question