pgfkeys and nicematrix calculate with pgfkeys and use in nicematrix preamble

Question

I have the following:

\documentclass[10pt, a4paper]{article}

\usepackage{nicematrix}

\pgfkeys{
        /tikz/gaussenv/.cd,
        % column number
        col/.initial=1,
        colC/.initial=4,
}

\newenvironment{gaussMatrix}[1][]%
{
        \pgfkeys{/tikz/gaussenv/.cd, #1}
        \pgfkeys{/tikz/gaussenv/colC=\pgfmathparse{int(\pgfkeysvalueof{/tikz/gaussenv/col}-1)}\pgfmathresult}
        %\pgfkeysvalueof{/tikz/gaussenv/colC}
        \begin{pNiceArray}[name=mymatrix]{*{\pgfkeysvalueof{/tikz/gaussenv/colC}}{C}|C}
        }%
        {
        \end{pNiceArray}
}


\begin{document}
\begin{align*}
        \begin{gaussMatrix}[col=5,colC=4] %number of colums in total, number of columns left of the line
                1 & 1 & 1 & 1 & 1 \\
                2 & 2 & 2 & 2 & 2 \\
                3 & 3 & 3 & 3 & 3 \\
                4 & 4 & 4 & 4 & 4 \\
                5 & 5 & 5 & 5 & 5 \\
        \end{gaussMatrix}
\\
\end{align*}

\end{document}

But somehow nicematrix doesn't like the output of pgfkeys. Without the calculation somehow it works, but I'd like to remove it that the total number of columns -1 has to be specified (even though this is easy to calculate).

Does someone know why this does not work and maybe a way to fix it?

Answer 1

You need to distinguish between some combination of commands that can be used to typeset a number, and some macro that can be used to store that number. You can use \pgfmathsetmacro to create a macro:

\documentclass[10pt, a4paper]{article}

\usepackage{nicematrix}

\pgfkeys{
        /tikz/gaussenv/.cd,
        % column number
        col/.initial=1,
        colC/.initial=4,
}

\newenvironment{gaussMatrix}[1][]%
{
        \pgfkeys{/tikz/gaussenv/.cd, #1}
        \pgfmathsetmacro{\mycolC}{int(\pgfkeysvalueof{/tikz/gaussenv/col}-1)}
        \pgfkeys{/tikz/gaussenv/colC=\mycolC}
        \begin{pNiceArray}[name=mymatrix]{*{\pgfkeysvalueof{/tikz/gaussenv/colC}}{C}|C}
        }%
        {
        \end{pNiceArray}
}


\begin{document}
\begin{align*}
        \begin{gaussMatrix}[col=5,colC=4] %number of colums in total, number of columns left of the line
                1 & 1 & 1 & 1 & 1 \\
                2 & 2 & 2 & 2 & 2 \\
                3 & 3 & 3 & 3 & 3 \\
                4 & 4 & 4 & 4 & 4 \\
                5 & 5 & 5 & 5 & 5 \\
        \end{gaussMatrix}
\\
\end{align*}

\end{document}

This assumes that you have a reason to store the result in a pgf key. If this is not the case, you can use a shorter code.

\documentclass[10pt, a4paper]{article}

\usepackage{nicematrix}

\pgfkeys{
        /tikz/gaussenv/.cd,
        % column number
        col/.initial=1,
        colC/.initial=4,
}

\newenvironment{gaussMatrix}[1][]%
{
        \pgfkeys{/tikz/gaussenv/.cd, #1}
        \begin{pNiceArray}[name=mymatrix]{*{\the\numexpr\pgfkeysvalueof{/tikz/gaussenv/col}-1}{C}|C}
        }%
        {
        \end{pNiceArray}
}


\begin{document}
\begin{align*}
        \begin{gaussMatrix}[col=5,colC=4] %number of colums in total, number of columns left of the line
                1 & 1 & 1 & 1 & 1 \\
                2 & 2 & 2 & 2 & 2 \\
                3 & 3 & 3 & 3 & 3 \\
                4 & 4 & 4 & 4 & 4 \\
                5 & 5 & 5 & 5 & 5 \\
        \end{gaussMatrix}
\\
\end{align*}

\end{document}