How to add vertical space and center the entries of a last row of a table

Question

I currently have a table in latex that looks like:

\begin{tabular}{c|ll}
  \hline
 Unit (i) &  \multicolumn{2}{c}{The combinations} \\ 
  i & $(-1,-1,-1,-1)$ & $(-1,-1,+1,+1)$  \\ 
  \hline
  1 & $Y_{1}(-1,-1,-1,-1)$ & $Y_{1}(-1,-1,+1,+1)$  \\ 
  2 & $Y_{2}(-1,-1,-1,-1)$ & $Y_{2}(-1,-1,+1,+1)$  \\ 
  3 & $Y_{3}(-1,-1,-1,-1)$ & $Y_{3}(-1,-1,+1,+1)$  \\ 
  4 & $Y_{4}(-1,-1,-1,-1)$ & $Y_{4}(-1,-1,+1,+1)$  \\ 
  5 & $Y_{5}(-1,-1,-1,-1)$ & $Y_{5}(-1,-1,+1,+1)$  \\ 
  \dotfill & \dotfill & \dotfill \\ 
  N & $Y_{N}(-1,-1,-1,-1)$ & $Y_{N}(-1,-1,+1,+1)$  \\ 
   \hline
   Average & $\bar{Y}(-1,-1,-1,-1)$ & $\bar{Y}(-1,-1,+1,+1)$  \\ 
    \hline
\end{tabular}

You can see that the last row has the average "bar" symbol touching the line created by hline. Is there a way to create more space in the last row, or possible add more vertical space to the other rows, without defining new commands? Thanks!

Answer 1

I'm not sure I think that the structure of your table is optimal, but I will leave that aside when answering on the vertical space.

I would suggest using the booktabs package and then use \toprule, \midrule and \bottomrule. Thus, first of all add

\usepackage{booktabs}

to your preamble. Next, try this table:

\begin{tabular}{cll}
\toprule
Unit (i) &  \multicolumn{2}{c}{The combinations} \\ 
i & $(-1,-1,-1,-1)$ & $(-1,-1,+1,+1)$  \\ 
\midrule
1 & $Y_{1}(-1,-1,-1,-1)$ & $Y_{1}(-1,-1,+1,+1)$  \\ 
2 & $Y_{2}(-1,-1,-1,-1)$ & $Y_{2}(-1,-1,+1,+1)$  \\ 
3 & $Y_{3}(-1,-1,-1,-1)$ & $Y_{3}(-1,-1,+1,+1)$  \\ 
4 & $Y_{4}(-1,-1,-1,-1)$ & $Y_{4}(-1,-1,+1,+1)$  \\ 
5 & $Y_{5}(-1,-1,-1,-1)$ & $Y_{5}(-1,-1,+1,+1)$  \\ 
\cdotfill & \cdotfill & \cdotfill \\ 
$N$ & $Y_{N}(-1,-1,-1,-1)$ & $Y_{N}(-1,-1,+1,+1)$  \\ 
\midrule
Average & $\strut\bar{Y}(-1,-1,-1,-1)$ & $\bar{Y}(-1,-1,+1,+1)$  \\ 
\bottomrule
\end{tabular}

Notice that I have also removed a vertical line and changed the \dotfill to \cdotfill. The \cdotfill command I used was stolen from this answer.

\makeatletter
\newcommand\cdotfill{%
  \leavevmode\cleaders\hb@xt@.44em{\hss$\cdot$\hss}\hfill\kern\z@
}
\makeatother

If you want the \cdotfill, this code should also go to the preamble.

The result can be seen in the picture below. Your table above, my variant below.

Answer 2

Two suggestions:

• Use judiciously placed typographic struts to improve the vertical spacing above and below the various horizontal lines. Note that I wouldn't increase the value of \arraystretch (default value: 1.0), as doing so will insert more vertical whitespace in all rows, and not just in those that are adjacent to a horizontal line.

• Since most of the material in the table is math-y, consider using an array environment instead of a tabular environment; if nothing else, making this switch lets you eliminate about 32 $ symbols, greatly de-cluttering the code. Also, consider right-aligning rather than centering the two data columns.

\documentclass{article}
\usepackage{amsmath} % for "\text" macro

%% Define a few struts
%% (from code by Claudio Beccari in *TeX and TUG News*, Vol. 2, 1993)
\newcommand\Tstrut{\rule{0pt}{2.9ex}}       % "top" strut
\newcommand\Bstrut{\rule[-1.2ex]{0pt}{0pt}} % "bottom" strut
\newcommand\TBstrut{\Tstrut\Bstrut}         % "top-and-bottom" strut

\begin{document}

$\begin{array}{c|rr}
\hline
 \text{Unit ($i$)}\Tstrut &  \multicolumn{2}{c}{\text{The combinations}} \\ 
  i\Bstrut & (-1,-1,-1,-1) & (-1,-1,+1,+1)  \\ 
\hline
  1\Tstrut & Y_{1}(-1,-1,-1,-1) & Y_{1}(-1,-1,+1,+1)  \\ 
  2 & Y_{2}(-1,-1,-1,-1) & Y_{2}(-1,-1,+1,+1)  \\ 
  3 & Y_{3}(-1,-1,-1,-1) & Y_{3}(-1,-1,+1,+1)  \\ 
  4 & Y_{4}(-1,-1,-1,-1) & Y_{4}(-1,-1,+1,+1)  \\ 
  5\Bstrut & Y_{5}(-1,-1,-1,-1) & Y_{5}(-1,-1,+1,+1)  \\ 
  \dotfill & \dotfill & \dotfill \\ 
  N & Y_{N}(-1,-1,-1,-1) & Y_{N}(-1,-1,+1,+1)\Bstrut  \\ 
\hline
  \text{Average}\TBstrut & \bar{Y}(-1,-1,-1,-1) & \bar{Y}(-1,-1,+1,+1)  \\ 
\hline
\end{array}$

\end{document}