Trouble with formatting a tabularx environment

Question

I've been trying to format a table without success. I've followed several suggestions that I found in other answers but never manage to fully adapt it.

This is one of the examples I tried:

\documentclass{article}
\usepackage{booktabs, tabularx}
\begin{document}
\begin{center}
\begin{tabularx}{\linewidth}{cr*{6}{c}}
\toprule    
Probe & MW \newline (g/mol) & R \newline (nm) & \multicolumn{4}{c}{V (mL/g)} & K \newline (--) \\ 
\cmidrule(lr){4-7}
    &  &   & 1 & 2 & 3 & avg. &   \\
\midrule
    Label 1&   400        &   0.00      &   0.00     &  2.34    & 12.00  & 1.32 $\pm$ 0.42  & 1.00  \\
    Label 2&   10000      &   1.50      &   0.99     &  3.00    & 15.00  & 1.32 $\pm$ 0.42  & 1.00  \\
    Label 3&   500000     &   18.45     &   0.99     &  2.00    & 20.00  & 1.32 $\pm$ 0.42  & 1.00  \\
\bottomrule
\end{tabularx}
\end{center}
\end{document}

A things to be fixed but I haven't been able to:

• The names in the header should be centered vertically and I'd prefer the units in a different line.
• There seems to be an empty column at the end?
• bonus: How can I add a footnote to make a comment on one value? tried adding \footnotesize{} but the table and the footnote end up in different places.

Overall I just want a decent and simple graph but can't see h

Answer 1

You don't need tabularx, which is the wrong tool for a numeric table. Use tabular* and siunitx facilities.

I provide two realizations, the second one without extending the table up to the margins, which seems better.

\documentclass{article}
\usepackage{booktabs,siunitx}

\sisetup{separate-uncertainty}

\begin{document}

\begin{table}[htp]

\caption{Something that describes the table}\label{whatever}

\setlength{\tabcolsep}{0pt}
\begin{tabular*}{\linewidth}{
 @{\extracolsep{\fill}}
 l
 S[table-format=6.0,group-four-digits]
 S[table-format=2.2]
 S[table-format=1.2]
 S[table-format=1.2]
 S[table-format=2.2]
 S[table-format=1.2(2)]
 S[table-format=1.2]
}
\toprule
Probe & {MW} & R & \multicolumn{4}{c}{V (\si{mL/g})} & {K} \\ 
\cmidrule{4-7}
& {(\si{g/mol})} & {(\si{nm})} & {1} & {2} & {3} & {avg.} & {(--)} \\ 
\midrule
Label 1 &    400 &  0.00 & 0.00 & 2.34 & 12.00 & 1.32 \pm 0.42 & 1.00  \\
Label 2 &  10000 &  1.50 & 0.99 & 3.00 & 15.00 & 1.32 \pm 0.42 & 1.00  \\
Label 3 & 500000 & 18.45 & 0.99 & 2.00 & 20.00 & 1.32 \pm 0.42 & 1.00  \\
\bottomrule
\end{tabular*}

\end{table}

\begin{table}[htp]
\centering

\caption{Something that describes the table}\label{whatever2}

\begin{tabular}{
 @{}
 l
 S[table-format=6.0,group-four-digits]
 S[table-format=2.2]
 S[table-format=1.2]
 S[table-format=1.2]
 S[table-format=2.2]
 S[table-format=1.2(2)]
 S[table-format=1.2]
 @{}
}
\toprule
Probe & {MW} & R & \multicolumn{4}{c}{V (\si{mL/g})} & {K} \\ 
\cmidrule{4-7}
& {(\si{g/mol})} & {(\si{nm})} & {1} & {2} & {3} & {avg.} & {(--)} \\ 
\midrule
Label 1 &    400 &  0.00 & 0.00 & 2.34 & 12.00 & 1.32 \pm 0.42 & 1.00  \\
Label 2 &  10000 &  1.50 & 0.99 & 3.00 & 15.00 & 1.32 \pm 0.42 & 1.00  \\
Label 3 & 500000 & 18.45 & 0.99 & 2.00 & 20.00 & 1.32 \pm 0.42 & 1.00  \\
\bottomrule
\end{tabular}

\end{table}

\end{document}

You can center the header in the first column by using \multicolumn{1}{c}{Probe} (or \multicolumn{1}{@{}c}{Probe} for the second realization, where we remove the padding on the left of the first column).

I added also a trick for pulling the units nearer the header.

\documentclass{article}
\usepackage{amsmath,booktabs,siunitx}

\sisetup{separate-uncertainty}

\newcommand{\tabhead}[1]{%
  \smash[b]{%
    \begin{tabular}[t]{@{}c@{}}#1\end{tabular}%
  }%
}

\begin{document}

\begin{table}[htp]

\caption{Something that describes the table}\label{whatever}

\setlength{\tabcolsep}{0pt}
\begin{tabular*}{\linewidth}{
 @{\extracolsep{\fill}}
 l
 S[table-format=6.0,group-four-digits]
 S[table-format=2.2]
 S[table-format=1.2]
 S[table-format=1.2]
 S[table-format=2.2]
 S[table-format=1.2(2)]
 S[table-format=1.2]
}
\toprule
\multicolumn{1}{c}{Probe} &
{\tabhead{MW \\ (\si{g/mol})}} &
{\tabhead{R \\ (\si{nm})}} &
\multicolumn{4}{c}{V (\si{mL/g})} &
{\tabhead{K \\ (--)}} \\ 
\cmidrule{4-7}
&&& {1} & {2} & {3} & {avg.} \\
\midrule
Label 1 &    400 &  0.00 & 0.00 & 2.34 & 12.00 & 1.32 \pm 0.42 & 1.00  \\
Label 2 &  10000 &  1.50 & 0.99 & 3.00 & 15.00 & 1.32 \pm 0.42 & 1.00  \\
Label 3 & 500000 & 18.45 & 0.99 & 2.00 & 20.00 & 1.32 \pm 0.42 & 1.00  \\
\bottomrule
\end{tabular*}

\end{table}

\end{document}

Answer 2

Some suggestions:

• When using the tabularx environment, make sure to use at least one column of type X. For the table at hand, it seems OK to change the type of the first column from l to X. I'm assuming (hoping?!) that the "real" column labels will be more descriptive, and thus possibly also longer, than "Label 1", "Label 2", and "Label 3". If that's the case, it's useful to use the X column type for the first column as it allows automatic linebreaking. (The l column type does not.) In contrast, there would appear to be no scope for allowing line breaks in any of the other columns.

  The appearance of what looks like an empty column at the right-hand edge of your code is caused directly by the failure to use one or more columns of type X.

• As you've discovered, using \newline in a cell doesn't work. In the answer below, I propose a handy macro to typeset a header cell and associated units in a stacked format.

• Optional: Consider using the siunitx package to (a) typeset scientific units properly (via he package's \si macro) and (b) align the numbers in columns 2 and 3 on their (explicit or implicit) decimal markers (via the package's S column type).

\documentclass{article}
\usepackage{booktabs, tabularx, siunitx, xcolor}
\sisetup{per-mode=symbol,group-digits=false}

%% handy utility macro:
\newcommand\smalltab[1]{%
    \smash{\begin{tabular}[t]{@{}c@{}} #1 \end{tabular}}}

\begin{document}

\noindent
\textcolor{red}{Before}

\begin{center}
\begin{tabularx}{\linewidth}{@{} l r *{6}{c}}
\toprule    
Probe & MW \newline (g/mol) & R \newline (nm) & \multicolumn{4}{c}{V (mL/g)} & K \newline (--) \\ 
\cmidrule(lr){4-7}
    &  &   & 1 & 2 & 3 & avg. &   \\
\midrule
    Label 1&   400        &   0.00      &   0.00     &  2.34    & 12.00  & 1.32 $\pm$ 0.42  & 1.00  \\
    Label 2&   10000      &   1.50      &   0.99     &  3.00    & 15.00  & 1.32 $\pm$ 0.42  & 1.00  \\
    Label 3&   500000     &   18.45     &   0.99     &  2.00    & 20.00  & 1.32 $\pm$ 0.42  & 1.00  \\
\bottomrule
\end{tabularx}
\end{center}

\bigskip\noindent
\textcolor{red}{After}

\begin{center}
\begin{tabularx}{\linewidth}{@{} X
   S[table-format=6.0] S[table-format=2.2] *{5}{c} @{}}
\toprule    
Probe & \smalltab{MW\\(\si{\gram\per\mole})}
      & \smalltab{R\\(\si{\nano\meter})} 
      & \multicolumn{4}{c}{V (\si{\milli\liter\per\gram})} 
      & \smalltab{K\\(--)} \\ 
\cmidrule(lr){4-7}
& & & 1 & 2 & 3 & avg. & \\
\midrule
Label 1 & 400    & 0.00  & 0.00 &  2.34 & 12.00  & 1.32\,${\pm}$\,0.42  & 1.00  \\
Label 2 & 10000  & 1.50  & 0.99 &  3.00 & 15.00  & 1.32\,${\pm}$\,0.42  & 1.00  \\
Label 3 & 500000 & 18.45 & 0.99 &  2.00 & 20.00  & 1.32\,${\pm}$\,0.42  & 1.00  \\
\bottomrule
\end{tabularx}
\end{center}

\end{document}