Making a new command for tabular environments with flexible table sizes

Question

I'm trying to create essentially a "new command" or "new environment" with a tabular environment. Is there any possibility to make a simple command that allows me to enter the size of the table and its corresponding entries. For instance, I want to make a command that makes the first table and just change a few numbers to create the second table. How would I accomplish this? Please let me know and thank you.

\begin{document} 
\[
    \begin{tabular}{>{$}c<{$}|*{8}{>{$}c<{$}}}
    & E   & 2A   & B & 2C & 2D\\
    \hline
    \vrule height 12pt width 0pt
    \Gamma_1  &  (1)  &  (1)  & (1) & (1) & (1)\\
    \Gamma_2   & 1  & (1) & 1  & -1 &-1 \\
    \Gamma_3 & 1 & -1   & 1 & 1 & -1\\
    \Gamma_4   & 1   & -1  & 1  & (-1) & 1\\
    \Gamma_5 & (2) & 0 & (-2) & 0 & 0\\
    \end{tabular}
\]
\[
    \begin{tabular}{>{$}l<{$}|*{8}{>{$}l<{$}}}
    C_{3\si{v}}   & E   & C_3   & C_3^2 & \sv & \sv' & \sv'' \\
    \hline
    \vrule height 12pt width 0pt
    E  & E   & C_3   & C_3^2 & \sv & \sv' & \sv'' \\
    C_3   & C_3   & C_3^2 & E  & \sv'' & \sv & \sv' \\
    C_3^2 & C_3^2 & E   & C_3  & \sv' & \sv'' & \sv\\
    \sv   & \sv   & \sv'  & \sv''  & E & C_3 & C_3^2\\
    \sv' & \sv' & \sv'' & \sv & C_3^2 & E & C_3\\
    \sv'' & \sv'' & \sv & \sv' & C_3 &C_3^2 & E\\
    \end{tabular}
\]
\end{document}

Answer 1

Yes, it makes sense to define an environment for structures that are repeated more than twice in a document.

You should use array and not tabular, but that's essentially all. Find a better name than foo. The optional argument is for the alignment in the columns, default c.

\documentclass{article}
\usepackage{amsmath,array}

\newcommand{\sv}{\sigma_{v}}
\newcommand{\rowstrut}{\rule{0pt}{12pt}}

\newenvironment{foo}[2][c]
 {\begin{array}{#1|*{\value{MaxMatrixCols}}{#1}}#2\\\hline\rowstrut}
 {\end{array}}

\begin{document}

\[
\begin{foo}{& E & 2A & B & 2C & 2D}
  \Gamma_1 & (1) & (1) & (1)  & (1)  & (1) \\
  \Gamma_2 & 1   & (1) & 1    & -1   & -1  \\
  \Gamma_3 & 1   & -1  & 1    & 1    & -1  \\
  \Gamma_4 & 1   & -1  & 1    & (-1) & 1   \\
  \Gamma_5 & (2) & 0   & (-2) & 0    & 0   \\
\end{foo}
\]
\[
\begin{foo}[l]{C_{3v} & E & C_3 & C_3^2 & \sv & \sv' & \sv''}
  E     & E     & C_3   & C_3^2 & \sv   & \sv'  & \sv'' \\
  C_3   & C_3   & C_3^2 & E     & \sv'' & \sv   & \sv'  \\
  C_3^2 & C_3^2 & E     & C_3   & \sv'  & \sv'' & \sv   \\
  \sv   & \sv   & \sv'  & \sv'' & E     & C_3   & C_3^2 \\
  \sv'  & \sv'  & \sv'' & \sv   & C_3^2 & E     & C_3   \\
  \sv'' & \sv'' & \sv   & \sv'  & C_3   & C_3^2 & E     \\
\end{foo}
\]

\end{document}

I used MaxMatrixCols that's the same counter used for matrices in amsmath. You can use *{20}{c} as well.

I removed \si{v} as there is no unit with symbol “v” and every other ‘v’ in the table is in math italic.