multicol: column balancing only after a minimum number of lines?

Question

I am using multicol.sty for balanced columns on a small part of the page. Generally I want these columns to be balanced, but not if the resulting twocol part ist less than 3 lines in height. How can I do this? (By automation?)

MWE:

\documentclass{scrartcl}
\usepackage{multicol}
\parindent 0pt

\begin{document}

Some onecolumn text goes here on top of the page \ldots 

\begin{multicols}{2}
    This text is balanced into two columns, although it is very
    short. How can I prevent balancing below 3 lines minimum
    height?
\end{multicols}%

Some more onecolumn text goes here below the twocol part \ldots 

\end{document} 

So in this example I want all the twocol text to appear only in the left column.

Answer 1

Full automation is right now only possible with a code change. As a one-off it is easy: Before the environment set the counter unbalance to 2. This will enlarge the starting vertical size by 2 \baselineskips.

The counter will be reset to zero after each environment.

A more general solution that does it automatically could look like this:

\documentclass{scrartcl}
\usepackage[balancingshow]{multicol}
\parindent 0pt

%-------------------------------------------------------------------------------
\usepackage{regexpatch}

\newcounter{multicolminlines}
\setcounter{multicolminlines}{1}

\makeatletter
\xpatchcmd\balance@columns
   {\ifnum\dimen@<\topskip
     \mult@info\@ne
       {Start value
          \the\dimen@  \space ->
          \the\topskip \space (corrected)}%
     \dimen@\topskip
   \fi}
   {\skip@\c@multicolminlines\baselineskip
   \advance\skip@-\baselineskip
   \advance\skip@\topskip
   \ifnum\dimen@<\skip@
     \mult@info\@ne
       {Start value
          \the\dimen@  \space ->
          \the\skip@ \space (corrected)}%
     \dimen@\skip@
   \fi
   }
   {\typeout{Success!}}{\patchFAILED}
\makeatother
%-------------------------------------------------------------------------------

\begin{document}

Some onecolumn text goes here on top of the page \ldots 

\setcounter{multicolminlines}{3}
\begin{multicols}{2}
    This text is balanced into two columns, although it is very
    short. How can I prevent balancing below 3 lines minimum
    height?
\end{multicols}

Some more onecolumn text goes here below the twocol part \ldots 


\setcounter{multicolminlines}{2}
\begin{multicols}{2}
    This text is balanced into two columns, although it is very
    short. How can I prevent balancing below 3 lines minimum
    height?
\end{multicols}


\begin{multicols}{2}
    This text is balanced into two columns, although it is very
    short. 
\end{multicols}

\setcounter{multicolminlines}{1}
\begin{multicols}{2}
    This text is balanced into two columns, although it is very
    short. 
\end{multicols}

\end{document} 

If we apply this patch then we get the following output (note that I change the minimum number of lines for the various environments):