How to vertically align 'numbers' in a table? [pairs of numbers given as strings]

Question

I display two sorts of values (say, A and B) in one table. The values are generated in R and I automatically create strings like "A (B)", so all values of type B are put in parentheses and are appended to the values of A. As you can see from the resulting table, the spacing is not quite right, it depends on the number of digits of B:

\documentclass{article}

\usepackage{tabularx}
\usepackage{booktabs}

\begin{document}
\begin{tabular}{rr}
  \toprule
   27.8 ( 2.8) &  38.4 ( 3.1)\\
  126.8 (10.3) & 171.9 (11.2)\\
  \bottomrule
\end{tabular}
\end{document}

I am wondering what good ways are to fix this?

One option would be to check the number of digits of B and add \phantom{0} accordingly, or \ \, also does it. But I would be interested in whether it is possible to align the numbers without these 'hacks'. Ideally, I would like to keep the numbers as they are (for example, to be able to easily use the same table in non-LaTeX documents).

In theory, a solution could be to align the numbers according to two dots (like an alignat environment in comparison to align) . But I'm not sure whether this can be done (with siunitx (?))

This is what I found on this topic, but adding ~ is like the above (thus required adjustments of the table entries) and monospaced fonts ... hmmm... doesn't seem very elegant.

UPDATE

Trial after David's post:

\documentclass{article}

\usepackage{tabularx}
\usepackage{booktabs}
\usepackage{dcolumn}
\usepackage{siunitx}

\begin{document}

With \texttt{dcolumn}:
\par\medskip
\begin{tabular}{rD{.}{.}{-1}}
  \toprule
   27.8 &  38.4 (2.3)\\
  126.8 & 171.9 (29.1)\\
  \bottomrule
\end{tabular}
\par\bigskip
With \texttt{siunitx}:
\par\medskip
\begin{tabular}{S
                S}
  \toprule
   27.8 &  38.4(3)\\
  126.8 & 171.9(1)\\
  \bottomrule
\end{tabular}
\par\bigskip
How it should look like:
\par\medskip
\begin{tabular}{rr}
  \toprule
   27.8 &  38.4 (\ \,2.3)\\
  126.8 & 171.9 (29.1)\\
  \bottomrule
\end{tabular}

\end{document}

Answer 1

add \usepackage{dcolumn} then you can replace r by D{.}{.}{-1} for columns centred on a . (There are other options, see the package documentation). siunitx package S column has similar features.

\documentclass{article}

\usepackage{booktabs}
\usepackage{dcolumn}


\begin{document}


\begin{tabular}{
D{.}{.}{3.2} 
D{.}{.}{3.1} @{\,}
D{.}{.}{3.2} 
 }
  \toprule
   27.8 &  38.4 &(2.3)\\
  126.8 & 171.9 &(29.1)\\
  \bottomrule
\end{tabular}

\end{document}

Or this version which doesn't require the extra &

\documentclass{article}

\usepackage{booktabs}
\usepackage{dcolumn}

\makeatletter
\newcolumntype{E}{>{\DDC}c}
\def\DDC#1(#2){\DC@..{3.2}#1\DC@end\,(\DC@..{2.1}#2\DC@end)}
\makeatother
\begin{document}


\begin{tabular}{
D{.}{.}{3.2} 
E
 }
  \toprule
   27.8 &  38.4 (2.3)\\
  126.8 & 171.9 (29.1)\\
  \bottomrule
\end{tabular}

\end{document}

With Colour:

\documentclass{article}

\usepackage{booktabs}
\usepackage{dcolumn,color}

\makeatletter

\newcolumntype{E}{>{\myDDC}c}
\def\myDDC\ignorespaces{\@ifnextchar!{\color{red}\@myDDC\@gobble}{\@myDDC}}
\def\@myDDC#1(#2){\DC@..{3.2}#1\DC@end\,(\DC@..{2.1}#2\DC@end)}

\newcolumntype{F}{>{\myDC}c<{\DC@end}}
\def\myDC\ignorespaces{\@ifnextchar!{\color{red}\@myDC\@gobble}{\@myDC}}
\def\@myDC{\DC@..{3.2}}

\makeatother
\begin{document}


\begin{tabular}{FE}
  \toprule
   27.8 & !38.4 (2.3)\\
  !126.8 & 171.9 (29.1)\\
  \bottomrule
\end{tabular}

\end{document}

Answer 2

Have you considered a monospace font for your table?

\documentclass{article}

\usepackage{tabularx}
\usepackage{booktabs}

\begin{document}

\texttt{
\begin{tabular}{rr}
  \toprule
   27.8 ( 2.8) &  38.4 ( 3.1)\\
  126.8 (10.3) & 171.9 (11.2)\\
  \bottomrule
\end{tabular}
}

\end{document}