Highlighting table cells

Question

I have a large (13x13) table in which I need to highlight a subset of cells. I know that I can set a background color to those cells using colortbl or xcolor. But I need to highlight the table without using color (it is a scientific paper, and the table should communicate its purpose without assuming the reader will have access to a color printer). Is there a way to do so? For example a circle around the cell?

Answer 1

Generally I agree with lockstep that circling might not be the best way to highlight text. In addition to his suggestions, you could also try using a light gray background.

Having said that, here is a way to circle text using TikZ:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{fit,shapes.geometric}

\newcounter{nodemarkers}
\newcommand\circletext[1]{%
    \tikz[overlay,remember picture] 
        \node (marker-\arabic{nodemarkers}-a) at (0,1.5ex) {};%
    #1%
    \tikz[overlay,remember picture]
        \node (marker-\arabic{nodemarkers}-b) at (0,0){};%
    \tikz[overlay,remember picture,inner sep=2pt]
        \node[draw,ellipse,fit=(marker-\arabic{nodemarkers}-a.center) (marker-\arabic{nodemarkers}-b.center)] {};%
    \stepcounter{nodemarkers}%
}

\begin{document}

\begin{tabular}{*6{c}}\hline
    Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\\hline
    bla   & bla   & \circletext{bla}   & bla   & bla   & bla \\
    bla   & bla   & bla   & bla   & bla   & bla \\ 
    ble   & ble   & ble   & bla   & \circletext{bla}   & bla \\ 
    bla   & bla   & bla   & bla   & bla   & bla \\ \hline
\end{tabular}

\end{document}

The \circletext command defines a node to the left and right of the text and then fits an ellipse around them. More fanciful graphics are of course possible, this is a rather basic example (since I do not know what your table looks like). Two LaTeX runs are necessary to have everything show up in the right place.

---

Edit: Here is an example of how to mark arbitrary blocks. Ellipses don't look good with large blocks, so it is using rounded rectangles instead:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{fit,shapes.misc}

\newcommand\marktopleft[1]{%
    \tikz[overlay,remember picture] 
        \node (marker-#1-a) at (0,1.5ex) {};%
}
\newcommand\markbottomright[1]{%
    \tikz[overlay,remember picture] 
        \node (marker-#1-b) at (0,0) {};%
    \tikz[overlay,remember picture,thick,dashed,inner sep=3pt]
        \node[draw,rounded rectangle,fit=(marker-#1-a.center) (marker-#1-b.center)] {};%
}

\begin{document}

\begin{tabular}{*6{c}}\hline
    Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\\hline
    bla   & bla   & \marktopleft{c1}bla   & bla   & bla   & bla \\
    bla   & bla   & bla   & bla   & bla   & bla \\ 
    ble   & ble   & ble   & bla   & bla\markbottomright{c1}   & bla \\ 
    bla   & bla   & bla   & bla   & bla   & bla \\ 
    bla   & \marktopleft{c2}bla   & bla   & bla   & bla\markbottomright{c2}   & bla \\ \hline
\end{tabular}

\end{document}

Answer 2

I cannot offer a "TeXnical" answer, only typographical advice: A circle put around a subset of cells within a large table may look like a superimposed figure unrelated to the table - in other words, it may be very confusing. Instead, I would try one of the following:

• Draw a rectangle around the particular cells (may still not look pretty);

• Use a raster as background;

• Typeset the cell content in bold or italic.

Answer 3

I think replacing the matrix with a TiKZ matrix would allow you to fit paths around groups of cells.

Answer 4

Here is a solution with the use of the relatively new nicematrix package.

\documentclass{article}

\usepackage{nicematrix}
\usepackage{tikz}
\usetikzlibrary{fit}

\begin{document}
\begin{NiceTabular}{*6{c}}[name=MyTbl]
    \hline
    Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\\hline
    bla   & bla   & bla   & bla   & bla   & bla \\
    bla   & bla   & bla   & bla   & bla   & bla \\ 
    ble   & ble   & ble   & bla   & bla   & bla \\ 
    bla   & bla   & bla   & bla   & bla   & bla \\ 
    bla   & bla   & bla   & bla   & bla   & bla \\ \hline
    
    \CodeAfter
        \tikz \node[draw, dashed, rounded corners, inner ysep=0.3mm, rectangle, fit=(MyTbl-2-3) (MyTbl-4-5)] {};
        \tikz \node[draw, dashed, rounded corners, inner ysep=0.3mm, rectangle, fit=(MyTbl-6-2) (MyTbl-6-5)] {};
\end{NiceTabular}

\bigskip
Table with a bit more space around the rows:

{%
\NiceMatrixOptions{cell-space-limits = 2mm}
\begin{NiceTabular}{*6{c}}[name=MyTbl2]
    \hline
    Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\\hline
    bla   & bla   & bla   & bla   & bla   & bla \\
    bla   & bla   & bla   & bla   & bla   & bla \\ 
    ble   & ble   & ble   & bla   & bla   & bla \\ 
    bla   & bla   & bla   & bla   & bla   & bla \\ 
    bla   & bla   & bla   & bla   & bla   & bla \\ \hline
    
    \CodeAfter
        \tikz \node[draw, dashed, rounded corners, inner ysep=-1mm, rectangle, fit=(MyTbl2-2-3) (MyTbl2-4-5)] {};
        \tikz \node[draw, dashed, rounded corners, inner ysep=-1mm, rectangle, fit=(MyTbl2-6-2) (MyTbl2-6-5)] {};
\end{NiceTabular}%
}
\end{document}

The nicematrix package associates a tikz node with every cell of the table and it's possible to use these nodes to draw different shapes. The nodes can be accessed by name-i-j where name is the name given to the table through the optional argument available in the environment and i and j are the numbers of row and column.

Answer 5

In addition to putting a frame around table cells, you might also need to add color and/or a note number. At least, it was my case.

I started out with the code from @Caramdir's answer and expanded on it. Here are my commands:

• \mtl{<note number>} -- mark top left corner
• \mbr[<optional fill color>]{<note number>} -- mark bottom right corner

If cells have longer text (see note 2), the frame might cross it. To avoid that, use a spacing macro as done in note 4 (\quad\mbr...).

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{calc,fit,shapes.misc}

% Mark top left
\newcommand\mtl[2][none]{%
    \tikz[overlay,remember picture] 
        \node (marker-#2-a) at (0,0.9ex) {};%
}

% Mark bottom right
\newcommand\mbr[2][none]{%
    \tikz[overlay,remember picture] 
        \node (marker-#2-b) at (0.2ex,0.3ex) {};%
    \tikz[overlay,remember picture,thick,inner sep=5pt]
        \node[draw,
              blend mode=darken,
              rectangle,
              rounded corners,
              fill=#1,
              fit=(marker-#2-a.center) (marker-#2-b.center)] {};%
    \tikz[overlay,remember picture] 
    \path 
        let
          \p{mtl} = (marker-#2-a), \p{mbr} = (marker-#2-b)
        in
          % Tweak xshift and yshift values to change note number position
          [x=\x{mbr}, y=\y{mtl}, xshift=1em, yshift=0.5em]
          node[rounded corners,inner sep=2pt,fill=white,opacity=0.8,text opacity=1] at (1, 1) {\footnotesize{\textbf{#2}}};%
}

\begin{document}

\begin{tabular}{*5{c}}\hline
       Col 1 & Col 2 & Col 3 & Col 4 & Col 5 \\\hline
       bla  & bla        & bla              & bla  & \mtl{2}blabla \\
\mtl{1}bla  & bla        & bla              & bla  & bla\mbr{2} \\ 
       ble  & ble\mbr{1} & bla              & bla  & bla \\ 
       bla  & bla        & bla              & bla  & \mtl{4}blabla \\ 
\mtl{3}bla  & bla        & bla\mbr[cyan]{3} & bla  & bla\quad\mbr{4} \\ \hline
\end{tabular}

\end{document}