# Evenly distributing column widths

Consider the following hunk of code:

\begin{tabular}{| c | c | c | c | c | c | c | }
\cline{2-7}
\multicolumn{1}{c}{} & \multicolumn{3}{|c|}{Fantastical aardvarks}
& \multicolumn{3}{c|}{Spelunking elephants}\\
\hline
Foo bar & A & B & C & A & B & C\\
\hline
5 & 87 &  5 &  2 & 82 & 18 & 48\\
6  & 5 & 43 &  4 & 7 & 47 & 4\\
7 &  7 &  18 & 63 & 2 & 9 & 99\\
\hline
\end{tabular}


Is there a way to have the three columns under "Fantastical aardvarks" and, separately, under "Spelunking elephants" have widths that are evenly distributed?

I'm particularly interested in an automated way of doing this, without needing to directly specify column widths.

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You could use the tabularx environment instead of the tabular environment. The tabularx environment, made available by loading the tabularx package, provides a column type called "X" that should satisfy your professed need to have several equal-width columns. The first table in the MWE below explains how to do this.

There is one decision, however, that the author must make, i.e., which can't be automated entirely: How wide should the entire table be? Often, one simply sets this width to \textwidth (the width of the current textblock) and then lets tabularx determine how wide the individual columns of type X will be. For this MWE (which uses the default text width assigned by LaTeX), with some trial-and-error work I found that it's possible to specify the table's overall width as narrow as about 0.75\textwidth. For your actual document, you will need to play around with the table width setting to determine empirically what the narrowest possible table width may be.

Note also the use of the specifier \centering\arraybackslash before the X column type in the MWE. I've inserted this specifier as it appears that you want the contents of the columns to be centered. (By default, the contents of an X column are set "ragged-right".)

That said, I'd also like to very strongly encourage you to consider (i) getting rid of all vertical lines in the table and (ii) use the booktabs package to getter spacing above and below the various rules in the table. This package provides the commands \toprule, \bottomrule, \midrule, and \cmidrule; how to use them is explained in the second part of the MWE below. Note that it's possible to left-trim and/or right-trim a \cmidrule -- something that's quite impossible to achieve with \cline. Comparing the two forms of the table, I daresay that the overwhelming majority of readers will find the second form to be both more pleasing to look at and to be more easily understandable. :-)

\documentclass{article}
\usepackage{tabularx, booktabs}
\newcolumntype{Y}{>{\centering\arraybackslash}X}
\begin{document}

\noindent
First version: many vertical lines,
all horizontal lines of equal width,
spacing above\slash below horizontal lines unsatisfactory

\medskip\noindent
\begin{tabularx}{0.75\textwidth}{|c *{6}{|Y}|}

\cline{2-7}
\multicolumn{1}{c|}{}
& \multicolumn{3}{c|}{Fantastical aardvarks}
& \multicolumn{3}{c|}{Spelunking elephants}\\
\hline
Foo bar & A & B & C & A & B & C\\
\hline
5  & 87 &  5 &  2 & 82 & 18 & 48\\
6  &  5 & 43 &  4 &  7 & 47 &  4\\
7  &  7 & 18 & 63 &  2 &  9 & 99\\
\hline
\end{tabularx}

\bigskip\noindent
Second version: no vertical lines,
widths of horizontal lines vary,
spacing above/below horizontal lines satisfactory

\medskip\noindent
\begin{tabularx}{0.75\textwidth}{c *{6}{Y}}
\toprule
Foo bar
& \multicolumn{3}{c}{Fantastical aardvarks}
& \multicolumn{3}{c}{Spelunking elephants}\\
\cmidrule(lr){2-4} \cmidrule(l){5-7}
& A & B & C & A & B & C\\
\midrule
5  & 87 &  5 &  2 & 82 & 18 & 48\\
6  &  5 & 43 &  4 &  7 & 47 &  4\\
7  &  7 & 18 & 63 &  2 &  9 & 99\\
\bottomrule
\end{tabularx}
\end{document}


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Thanks! One followup: you've specified that you need to set the width of the entire table. Is there a way to do this without that specification? Ideally, for a smaller table, I'd rather it not be that wide. Or is specifying the entire width worth the effort for the better column spacing? –  Eli Lansey Jun 20 '12 at 19:52
To make the vertical rules line up, rather use \multicolumn{1}{c|}{} & \multicolumn{3}{c|}{Fantastical aardvarks} & \multicolumn{3}{c|}{Spelunking elephants}. @EliLansey: You can use something smaller than \textwidth (or \linewidth), like .5\linewidth for a 50% width table. –  Werner Jun 20 '12 at 19:54
I suppose the X column widths will have to be at least 1/3 of the max of the string lengths of "Fantastical aardvarks" and "Spelunking elephants". (However, in your actual table you will have different entries, right?!) The minimum table width will also depend on factors such as the font and font size in use. Unless you have lots and lots of tables of this sort, you're probably best off going the trial-and-error route, i.e., try out 0.8\textwdith, 0.75\textwidth, etc until the table doesn't look right. –  Mico Jun 20 '12 at 19:59
@Werner -- thanks, I'll correct the code to incorporate your suggestions! –  Mico Jun 20 '12 at 20:00
@Werner I'm not sure I understand your first sentence. –  Eli Lansey Jun 20 '12 at 20:00
\documentclass{article}
\usepackage{tabularx,ragged2e}
\usepackage{booktabs}

\begin{document}

{\tabcolsep=0pt\def\arraystretch{1.3}
\begin{tabularx}{250pt}{c *6{>{\Centering}X}}\toprule
& \multicolumn{3}{c}{Fantastical aardvarks}   & \multicolumn{3}{c}{Spelunking elephants}
\tabularnewline \cmidrule(lr){2-4}\cmidrule(l){5-7}
Foo bar & A & B & C & A & B &  C \tabularnewline \midrule
5  & 87 &  5 &  2 & 82 & 18 & 48 \tabularnewline
6  &  5 & 43 &  4 &  7 & 47 & 4 \tabularnewline
7  &  7 & 18 & 63 &  2 &  9 & 99 \tabularnewline\bottomrule
\end{tabularx}}

\end{document}


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