Latex label right and left side of augmented matrix

Question

How do I label both the right and left side of a augmented matrix ?

begin{document}    
    \[
\left[
\begin{array}{ccc|c}
a & b & c & d\\
a & b & c & d\\
a & b & c &d \\
\end{array}
\right]
[\begin{array}{l}
R_{1}  \\
R_{2a}  \\
R_{3a} 
\end{array}
\]
\end{document}

I have tried this which allows me to label the right side but not sure how to label the left

Answer 1

Perhaps the following works for you:

\documentclass{article}

\usepackage{array}

\newenvironment{rowlabels}{
  \begin{array}{ @{} >{\scriptstyle}l @{} }
}{
  \end{array}
}

\begin{document}    

\[
  \begin{rowlabels}
    L_1 \\ L_{2a} \\ L_{3a}
  \end{rowlabels}
  \left[
    \begin{array}{ @{} c c c | c @{} }
      a & b & c & d \\
      a & b & c & d \\
      a & b & c & d \\
    \end{array}
  \right]
  \begin{rowlabels}
    R_1 \\ R_{2a} \\ R_{3a} 
  \end{rowlabels}
\]

\end{document}

The new environment rowlabels sets a regular array with the elements in \scriptstyle.

Answer 2

\documentclass{article}
\usepackage{blkarray}
\begin{document}

$\begin{blockarray}{c[ccc|c]c}
 L_1 & a & b & c & d & R_1\\
 L_2 & a & b & c & d & R_2\\
 L_3 & a & b & c & d & R_3\\
 L_4 & a & b & c & d & R_4\\
\end{blockarray}$

\end{document}