Bold entries in table with S column type

Question

Inspired by the following post \bfseries and alignment in table, I want to create a table where some of the entries are highlighted in bold, and further, the numbers should be aligned on the dot. I defined the boldentry command as desribed on the post, but for some reason the numbers are not perfectly aligned in this case. What is the problem in the code below?

\documentclass[b5paper,10pt,authoryear,longnamesfirst]{memoir}
\usepackage{booktabs,siunitx}
\usepackage[flushleft]{threeparttablex}
\newcommand{\MS}[1] {
    \multicolumn{1}{c}{#1}}
\newcommand{\boldentry}[2]{%
    \multicolumn{1}{S[table-format=#1,
                mode=text,
                text-rm=\fontseries{b}\selectfont
               ]}{#2}}
\begin{document}

\sisetup{detect-weight=true,detect-inline-weight=math}

\begin{table}
\scriptsize
\caption{A caption}
\begin{threeparttable}
\begin{tabular*}{\textwidth}{l@{\extracolsep{\fill}}*{9}{S[table- 
    format=1.3]}}
\toprule
        & \MS{A} & \MS{B} & \MS{C} & \MS{D} & \MS{E} & \MS{F} & \MS{G} & 
          \MS{H} & \MS{I}\\
\midrule

     A & \boldentry{1.3}{1.004}&\boldentry{1.3}{1.000}&\boldentry{1.3} 
     {1.008}&\boldentry{1.3}{1.000}&\boldentry{1.3}{0.989}&\boldentry{1.3} 
     {1.008}&1.070  & \boldentry{1.3}{0.981}&1.025\\

     B & 1.025  & 1.012  & 1.016  & \boldentry{1.3}{1.000}&\boldentry{1.3} 
     {0.967}&\boldentry{1.3}{0.968}&\boldentry{1.3}{0.982}&\boldentry{1.3} 
     {0.961}&1.077\\

     C& 1.009  & 1.001  & 1.002  & 1.000  & 0.986  & 0.985  & 0.991  & 
     \boldentry{1.3}{0.973}&0.998\\

     D & 1.009  & 1.010  & 1.001  & 1.000  & 0.951  & 0.959  & 0.975  & 
     \boldentry{1.3}{0.931}&1.015\\
    \bottomrule

\end{tabular*}
\begin{tablenotes}
\setlength\labelsep{0pt}
\scriptsize
\item A footnote  
\end{tablenotes}
\end{threeparttable}
\end{table}

\end{document}

Answer 1

i remove your definition \newcommand{\boldentry}[2]{...}, add the package etoolbox for robust new command \B which is used to indicate the cells that have bold faced numbers. LL CHanges in comparison to your mwe are indicated in code by % <--:

\documentclass[b5paper,10pt,authoryear,longnamesfirst]{memoir}
\usepackage{booktabs}
\newcommand\mcc[1]{\multicolumn{1}{c}{#1}} % instead of \MS. you can still use your command ...
\usepackage{siunitx}
\usepackage[flushleft]{threeparttablex}

\usepackage{etoolbox}           % <--
\renewcommand{\bfseries}{\fontseries{b}\selectfont} % <--
\robustify\bfseries             % <--
\newrobustcmd{\B}{\bfseries}    % <--


\begin{document}
    \begin{table}
    \small
    \caption{A caption}
    \setlength\tabcolsep{0pt}
\begin{threeparttable}
\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}
        l
    *{9}{S[detect-weight,   % <--
           mode=text,       % <--
           table-format=1.3]}}
\toprule
    & \mcc{A}   & \mcc{B}   & \mcc{C}   & \mcc{D}   & \mcc{E}
    & \mcc{F}   & \mcc{G}   & \mcc{H}   & \mcc{I}       \\
\midrule
A   & \B 1.004  & \B 1.000  & \B 1.008  & \B 1.000  & \B 0.989
    & \B 1.008  &    1.070  & \B 0.981  &    1.025      \\
B   &   1.025   &    1.012  &    1.016  & \B 1.000  & \B 0.967
    & \B 0.968  & \B 0.982  & \B 0.961  &    1.077      \\
C   &    1.009  &    1.001  &    1.002  &    1.000  &    0.986
    &    0.985  &    0.991  & \B 0.973  &    0.998      \\
D   &    1.009  &    1.010  &    1.001  &    1.000  & 0.951
    &    0.959  &    0.975  & \B 0.931  &    1.015      \\
    \bottomrule
\end{tabular*}
\begin{tablenotes}
\setlength\labelsep{0pt}
\scriptsize
\item A footnote
\end{tablenotes}
\end{threeparttable}
\end{table}

\end{document}