Align text in a new command

Question

So I've been looking to align text in a custom matrix that is already made smaller. See link below for reference.

https://tex.stackexchange.com/a/59080/220808

In a \begin{pmatrix*} I'd simply put a [l] to align the numbers on the left, yet this is not that straight forward in a newcommand. Can somebody help me out?

I use this in my .sty file:

\newcommand{\colvec}[2][.8]{%
  \scalebox{#1}{%
    \renewcommand{\arraystretch}{.8}%
    $\begin{bmatrix}#2\end{bmatrix}$%
  }
}

With in the Equation I use:

\colvec[0.9]{
      -8.6831 \times 10^{-2}&-2.4059 \times 10^{-4}&-3.7120&1.0337 \times 10^{-1}\\
      6.3872 \times 10^{-1}&4.5360 \times 10^{-3}&-2.4419 \times 10^{1}&3.7390 \times 10^{-1}\\
      -1.1624&-5.3189 \times 10^{-2}&-5.8483 \times 10^{1}&1.0665        
    }  

The initial matrix would be:

\begin{pmatrix*}[l]
      -8.6831 \times 10^{-2}&-2.4059 \times 10^{-4}&-3.7120&1.0337 \times 10^{-1}\\
      6.3872 \times 10^{-1}&4.5360 \times 10^{-3}&-2.4419 \times 10^{1}&3.7390 \times 10^{-1}\\
      -1.1624&-5.3189 \times 10^{-2}&-5.8483 \times 10^{1}&1.0665        
\end{pmatrix*}  

Answer 1

Assuming that you want to be able to control the alignment with a further optional argument, this is one possibility

\documentclass{article}

\usepackage{mathtools}

\makeatletter

\newcommand{\colvec}[1][.8]{%
   \begingroup
   \if\relax\detokenize{#1}\relax\def\@tempa{.8}\else\def\@tempa{#1}\fi
   \@colvec}

\newcommand{\@colvec}[2][c]{%
   \scalebox{\@tempa}{%
      \renewcommand{\arraystretch}{.8}%
      $\begin{bmatrix*}[#1]#2\end{bmatrix*}$}%
      \endgroup}

\makeatother


\begin{document}

\colvec{1\\-2\\3412}
\qquad
\colvec[][l]{1\\-2\\3412}
\qquad
\colvec[.6]{1\\-2\\3412}
\qquad
\colvec[.6][r]{1\\-2\\3412}

\end{document}