Improve intercolumn spacing of this table

Question

I'm trying to spruce up the appearance of this table:

\begin{tabular}{rr@{\hspace{2em}}rr@{\hspace{2em}}rr@{\hspace{2em}}rr}
\toprule
\multicolumn{2}{c@{\hspace{2em}}}{\textbf{Word C}}&
\multicolumn{2}{c@{\hspace{2em}}}{\textbf{Char C}}&
\multicolumn{2}{c@{\hspace{2em}}}{\textbf{Chess}}&
\multicolumn{2}{c}{\textbf{Matching}}\\
\multicolumn{2}{c@{\hspace{2em}}}{\textbf{9 trials}}&
\multicolumn{2}{c@{\hspace{2em}}}{\textbf{9 trials}}&
\multicolumn{2}{c@{\hspace{2em}}}{\textbf{12 trials}}&
\multicolumn{2}{c}{\textbf{12 trials}}\\
$N$&$V$&$N$&$V$&$N$&$V$&$N$&$V$\\
\midrule
10 &  1 & 12 &  3 & 16 &  3 & 4 & 0 \\
10 &  1 & 12 &  6 & 16 &  3 & 4 & 0 \\
10 &  1 & 12 &  9 & 16 &  5 & 4 & 1 \\
10 &  2 & 24 &  6 & 16 &  5 & 4 & 1 \\
% ... many more rows ...
\bottomrule
\end{tabular}

Here's what it currently looks like. The biggest problem is that there's too much horizontal space between each N column and the corresponding V column, and that space is of variable size among the four groups.

What I want is for there to be a fixed, small distance between each N column and the corresponding V column; a larger distance between the group headings; and the N/V column pairs to be centered under their heading. The numbers in each column should continue to be right-justified. How might I accomplish this?

Note: all the elided rows contain numbers and only numbers, and there are no three-digit or larger numbers.

Answer 1

Here's one, not wholly satisfactory solution.

\documentclass{article}
\usepackage{booktabs}
\newcommand\clap[1]{\hbox to0pt{\hss#1\hss}}
\newcommand\MC[1]{%
        \multicolumn{2}{c@{\hspace{2em}}}{\clap{\textbf{#1}}}%
}
\begin{document}
\begin{tabular}{rr@{\hspace{2em}}rr@{\hspace{2em}}rr@{\hspace{2em}}rr}
\toprule
\MC{Word C}&
\MC{Char C}&
\MC{Chess}&
\MC{Matching}\\
\MC{9 trials}&
\MC{9 trials}&
\MC{12 trials}&
\MC{12 trials}\\
$N$&$V$&$N$&$V$&$N$&$V$&$N$&$V$\\
\midrule
10 &  1 & 12 &  3 & 16 &  3 & 4 & 0 \\
10 &  1 & 12 &  6 & 16 &  3 & 4 & 0 \\
10 &  1 & 12 &  9 & 16 &  5 & 4 & 1 \\
10 &  2 & 24 &  6 & 16 &  5 & 4 & 1 \\
% ... many more rows ...
\bottomrule
\end{tabular}
\end{document}

Answer 2

\documentclass{article}

\usepackage{array,booktabs,ragged2e}
\newcommand\MC[1]{\multicolumn{2}{@{}l}{\textbf{#1}}}

\def\SP{\hspace{15mm}}
\begin{document}

\begin{tabular}{@{} rl @{\SP} rl @{\SP} rl @{\SP} rl@{}}\toprule
\MC{Word C}  &\MC{Char C}  &\MC{Chess}    &\MC{Matching}\\
\MC{9 trials}&\MC{9 trials}&\MC{12 trials}&\MC{12 trials}\\
$N$&$V$&$N$&$V$&$N$&$V$&$N$&$V$\\\midrule
 10 &  1 & 12 &  3 & 16 &  3 & 4 & 0 \\
 10 &  1 & 12 &  6 & 16 &  3 & 4 & 0 \\
 10 &  1 & 12 &  9 & 16 &  5 & 4 & 1 \\
 10 &  2 & 24 &  6 & 16 &  5 & 4 & 1 \\
% ... many more rows ...
\bottomrule
\end{tabular}

\end{document}

Answer 3

Here is a Plain version, you can change the \groupheadingskip and \columnsepskip to your liking:

\documentclass{article}
\newskip\groupheadingskip \groupheadingskip=2em
\newskip\columnsepskip    \columnsepskip=1em
\newskip\rowsepskip       \rowsepskip=3pt
\def\header#1{\multispan2\hidewidth\bf#1\hidewidth}
\begin{document}
\begin{table}
\vbox{\openup\rowsepskip\hrule height 1pt \medskip
  \divide\groupheadingskip by 2
  \halign{&\tabskip\columnsepskip\hskip\groupheadingskip\hfil$#$&
    \hfil$#$\hskip\groupheadingskip\cr
    \header{Word C}&  \header{Char C}&  \header{Chess}&    \header{Matching}\cr
    \header{9 trials}&\header{9 trials}&\header{12 trials}&\header{12 trials}\cr
    N&V&   N&V&   N&V&   N&V\cr
    \noalign{\smallskip\hrule\medskip}
    10&1&  12&3&  16&3&  4&0\cr
    10&1&  12&6&  16&3&  4&0\cr
    10&1&  12&9&  16&5&  4&1\cr
  }
  \medskip \hrule height 1pt
}
\end{table}
\end{document}

Answer 4

It seems to me that, to provide space for the header to spread without affecting the data, you need more columns for the headers to spill into. Therefore, I recommend the following:

[Edit: I've incorporated elements of Herbert's post to obtain improved spacing of the headings, and also to condense the answer.]

\newlength\intercol
\setlength\intercol{0em}
\newlength\mycolwidth
\setlength\mycolwidth{1em}
\newcommand\head[1]{\parbox{\mycolwidth}{\hfill $#1$}}
\newcommand\MC[1]{\multicolumn{4}{@{}c@{}}{\textbf{#1}}}

\begin{tabular}%
      {@{}crrc@{\hspace\intercol}crrc@{\hspace\intercol}crrc@{\hspace\intercol}crrc@{}}
\toprule
  \MC{Word C}   &  \MC{Char C}    &  \MC{Chess}      &  \MC{Matching}
\\
  \MC{9 trials}  &  \MC{9 trials}  &  \MC{12 trials}  &  \MC{12 trials}
\\
  & \head{N}&\head{V} &&& \head{N}&\head{V} &&& \head{N}&\head{V} &&& \head{N}&\head{V} &
\\
\midrule
&   10 &  1     &&&     12 &    3   &&& 16  &   3       &&& 4   &   0   \\
&   10 &  1     &&&     12 &    6   &&& 16  &   3       &&& 4   &   0   \\
&   10 &  1     &&&     12 &    9   &&& 16  &   5       &&& 4   &   1   \\
&   10 &  2     &&&     24 &    6   &&& 16  &   5       &&& 4   &   1   \\
% ... many more rows ...
\bottomrule
\end{tabular}

Output:

• The lengths \intercol and \mycolwidth serve to determine the spacing between the column-quadruplets and the width of the data columns (the middle pair of each column quadruplet). The lengths are set to what seem æsthetically pleasing to me. (For data headings of N and V, 1em is about the minimum before you have problems.)

• The macro \head is defined to force the data columns to have the same width (i.e. to further encourage uniformity of spacing, despite any non-uniformity of the data); this forces the header to have the width described by \mycolwidth, which is ideally the maximum width of all data in the table. The extra \hfill in the macro forces the headers to be right-aligned (as the \parbox breaks alignment).

Answer 5

Unsurprisingly (as I write it), I'd use siunitx for a table of numbers like this. For me

\documentclass{article}
\usepackage{booktabs,siunitx}
\begin{document}
\sisetup{table-format=2.0}
\begin{tabular}{SSSSSSSS}
\toprule
\multicolumn{2}{c}{\textbf{Word C}}&
\multicolumn{2}{c}{\textbf{Char C}}&
\multicolumn{2}{c}{\textbf{Chess}}&
\multicolumn{2}{c}{\textbf{Matching}}\\
\multicolumn{2}{c}{\textbf{9 trials}}&
\multicolumn{2}{c}{\textbf{9 trials}}&
\multicolumn{2}{c}{\textbf{12 trials}}&
\multicolumn{2}{c}{\textbf{12 trials}}\\
$N$&$V$&$N$&$V$&$N$&$V$&$N$&$V$\\
\midrule
10 &  1 & 12 &  3 & 16 &  3 & 4 & 0 \\
10 &  1 & 12 &  6 & 16 &  3 & 4 & 0 \\
10 &  1 & 12 &  9 & 16 &  5 & 4 & 1 \\
10 &  2 & 24 &  6 & 16 &  5 & 4 & 1 \\
% ... many more rows ...
\bottomrule
\end{tabular}

\end{document}

looks fine. I'm not entirely clear what you mean about the spacing: LaTeX includes some inter-column space as standard, and to me the table looks readable without additional space being added.

For reference, what I get is