Wrap text in table column header AND fit table width to pagewidth

Question

How do I get a table where the header in column 2 is wrapped, while keeping the width of the table = textwidth? As you can see from the attached figure, I have a long title for the 2nd column, which makes the column very wide, resulting in wrapping of the text (actual entries, not the title) in the first column. I guess in a more general sense, I want to prioritize wrapping of column titles over wrapping of actual column entries. (I am not stuck on using tabularx; I am happy to try any other package if it works.)

\documentclass[12pt]{report} 
\usepackage{tabularx} 

\begin{document}

\begin{table}[h]
\begin{tabularx}{\textwidth}{XXXX}
\hline
\multicolumn{4}{c}{xxx xx xxxx}                                                                                           \\ \hline
\textbf{miRNA}  & \multicolumn{1}{l}{\textbf{logFC (ABCDEF vs ABCFED)}} & \textbf{PValue} & \textbf{False Discovery Rate}    \\ \hline
abcd efg hijka  & -1.854                                                & 9.52E-11        & 8.41E-10                         \\
abcd efg hijka  & -1.815                                                & 3.38E-09        & 2.42E-08                         \\ \hline
\end{tabularx}
\end{table}
a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width

\end{document}

Answer 1

Here is a solution using the makecell package that enables pre-formatting of column heads and multine heads. I also used the booktabs package to have better-looking horizontal rules and a less tight vertical spacing. Finally numprint allows for scientific notations in cells.

\documentclass[12pt]{report}
\usepackage[utf8]{inputenc}
\usepackage{fourier}
\usepackage{array}
\usepackage{booktabs}
\usepackage{tabularx}
\usepackage{makecell}

\newcolumntype{Z}{ >{\centering\arraybackslash}X }

\renewcommand\theadfont{\bfseries}
%\renewcommand\theadalign{cc}
\usepackage[autolanguage, np]{numprint}

\begin{document}

\begin{table}[!h]
\setlength\tabcolsep{4pt}
\begin{tabularx}{\textwidth}{*{4}{Z}}
\toprule
\multicolumn{4}{c}{xxx xx xxxx}   \\
\midrule
\thead{miRNA}  & \thead{logFC \\ (ABCDEF vs \\ ABCFED) } & \thead{PValue} & \thead{False \\Discovery\\ Rate} \\%
\midrule
abcd efg hijka  & $-1.854$                                                & \np{9.52E-11}        & \np{8.41E-10}                         \\
abcd efg hijka  & $-1.815$                                                & \np{3.38E-09}        & \np{2.42E-08}                         \\
 \bottomrule
\end{tabularx}
\end{table}
a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width

\end{document} 

Answer 2

I would use siunitx and tabular* instead of tabularx, because you're so able to get perfect output for the numbers. The first example is how you can do with tabularx, but note that you would have to manually correct the input for numbers. With the siunitx approach you can just input numbers as they are.

\documentclass[12pt]{report}
\usepackage{tabularx}
\usepackage{siunitx}
\usepackage{booktabs}

\newcommand{\tabheader}[1]{%
  \bfseries
  \begin{tabular}{@{}c@{}}
  \strut#1\strut
  \end{tabular}%
}

\begin{document}

\begin{table}[htp]
\centering
\begin{tabularx}{\textwidth}{*{4}{>{\raggedright\arraybackslash}X}}
\hline
\multicolumn{4}{c}{xxx xx xxxx} \\
\hline
\textbf{miRNA}  & 
  \textbf{logFC (ABCDEF vs ABCFED)} & 
  \textbf{PValue} & 
  \textbf{False Discovery Rate} \\
\hline
abcd efg hijka  & -1.854 & 9.52E-11 & 8.41E-10 \\
abcd efg hijka  & -1.815 & 3.38E-09 & 2.42E-08 \\
\hline
\end{tabularx}
\end{table}

\begin{table}[htp]
\sisetup{
  exponent-product={},
  output-exponent-marker=\ensuremath{\mathrm{E}},
}
\centering
\begin{tabular*}{\textwidth}{
  @{\extracolsep{\fill}}
  l
  S[table-format=-1.3]
  S[table-format=1.2E-2]
  S[table-format=1.2E-2]
  @{}
}
\toprule
\multicolumn{4}{c}{xxx xx xxxx} \\
\midrule
\tabheader{miRNA}  & 
  \tabheader{logFC (ABCDEF\\ vs ABCFED)} & 
  \tabheader{PValue} & 
  \tabheader{False\\ Discovery\\ Rate} \\
\midrule
abcd efg hijka  & -1.854 & 9.52E-11 & 8.41E-10 \\
abcd efg hijka  & -1.815 & 3.38E-09 & 2.42E-08 \\
\bottomrule
\end{tabular*}
\end{table}
\end{document}

Answer 3

Use X columns only if needed:

\documentclass[12pt]{report} 
\usepackage{tabularx,ragged2e} 
\renewcommand\tabularxcolumn[1]{>{\RaggedRight}p{#1}}

\begin{document}

\begin{table}[h]
\begin{tabularx}{\textwidth}{@{} lXlX @{} }\hline
\multicolumn{4}{c}{xxx xx xxxx} \\ \hline
\textbf{miRNA}  & \textbf{logFC (ABCDEF vs ABCFED)} & \textbf{PValue} & \textbf{False Discovery Rate}    \\ \hline
abcd efg hijka  & -1.854                                                & 9.52E-11        & 8.41E-10                         \\
abcd efg hijka  & -1.815                                                & 3.38E-09        & 2.42E-08                         \\ \hline
\end{tabularx}
\end{table}
a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width a lot of text here to show text width

\end{document}