Highlight a table row with a rectangular overlay

Question

I am trying to highlight the row of a table by drawing a rectangle over that row. A wrinkle is that the code for the table is pre-written from external statistical software and then included in the main document using the \input command. For this reason, I'd like to avoid placing code within the table, if at all possible. I have included a simple example:

\documentclass{article}

\begin{document}

\begin{center}
\input{table.tex}
\end{center}

\end{document}

And the code for table.tex is:

\begin{tabular}{l*{3}{c}}
& A & B & C \\
\hline
1 & blah & blah & blah \\
2 & blah & blah & blah \\
3 & blah & blah & blah \\
\hline
\end{tabular}

I'd like to add a red rectangle (perhaps rounded) around the second row, possibly using tikz or some other solution. If it matters, the table will ultimately be in a beamer slide, but I figured that including that code was not necessary.

Answer 1

You could put the \input in a node and draw a rectangle relative to the corners of the node.

\begin{filecontents*}{table.tex}
\begin{tabular}{l*{3}{c}}
& A & B & C \\
\hline
1 & blah & blah & blah \\
2 & blah & blah & blah \\
3 & blah & blah & blah \\
\hline
\end{tabular}
\end{filecontents*}
\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{frame}
\begin{center}
\begin{tikzpicture}
\node (table) {\input{table.tex}};
\draw [red,ultra thick,rounded corners]
  ($(table.south west) !.3! (table.north west)$)
  rectangle 
  ($(table.south east) !.5! (table.north east)$);
\end{tikzpicture}
\end{center}
\end{frame}
\end{document}

Some explanation to the above code

There are several standard anchors on a node by default, denoted by compass directions, accessed with the syntax <node name>.<anchor>. For example will MyNode.north west be the top left corner of MyNode.

To get a coordinate between two existing coordinates you can use the TikZ library calc. This is described in section 13.5 Coordinate Calculations of the manual. It provides the syntax

($(<nodename or coordinate>) ! <factor> ! (<nodename or coordinate>)$)

Dollar signs indicate that a coordinate calculation should be done. The <factor> is a number saying how far, on the line between the two specified nodes, relative to the distance between the nodes, the point should be. For example,

($(0,0) !.3! (1,0)$)

is 30% of the way between (0,0) and (1,0), meaning (0.3,0).

In other words,

\draw [red,ultra thick,rounded corners]
  ($(table.south west) !.3! (table.north west)$)
  rectangle 
  ($(table.south east) !.5! (table.north east)$);

draws a rectangle from the point that is 30% of the distance from the lower left corner to the upper left corner, to the point that is halfway between the lower right and upper right corners.

Answer 2

Here's a sans-TikZ way of obtaining the rectangle via a coloured \fbox:

\documentclass{article}
\usepackage{xcolor}% http://ctan.org/pkg/xcolor
\newsavebox{\mytable}
\begin{document}

\begin{center}
\begin{lrbox}{\mytable}
\input{table.tex}
\end{lrbox}
%\setlength{\fboxrule}{2pt}% Modify rule width if necessary
\ooalign{%
  \hss\usebox{\mytable}\hss \cr
  {\color{red}%
   \fbox{\phantom{\rule[-5pt]{\dimexpr\wd\mytable+10pt}{\dimexpr\baselineskip+5pt}}}%
  }
}
\end{center}

\end{document}​

The table \input is stored in a box \mytable in order to obtain the width. The box is subsequently positioned with a 5pt overlap on either side of the table by setting a blank box of appropriate dimensions inside the coloured \fbox.

Within \ooalign, the table is centrred (since it's less wide than the 10pt-wider \fbox) using \hss...\hss. This is overprint with the coloured \fbox. Here is a quick course on \ooalign.

You could also reverse the sequence to use a shaded highlighting:

\documentclass{article}
\usepackage{xcolor}% http://ctan.org/pkg/xcolor
\newsavebox{\mytable}
\begin{document}

\begin{center}
\begin{lrbox}{\mytable}
\input{table.tex}
\end{lrbox}%
\setlength{\fboxrule}{2pt}% Modify rule width if necessary
\ooalign{%
  {\fcolorbox{red!50}{red!30}{%
     \phantom{\rule[-5pt]{\dimexpr\wd\mytable+10pt}{\dimexpr\baselineskip+5pt}}%
  }} \cr
  \hss\usebox{\mytable}\hss
}
\end{center}

\end{document}​