How to change rounding precision across rows in a table?

Question

I use the package siunitx to print tables. In the following table, I would like to have a different rounding precision and number of printed decimal places for each row.

\usepackage{siunitx}
\sisetup{   
        round-mode      = places,
        round-precision = 3,
        group-separator = {,},
        }
\begin{tabular}{l*{2}{S}}
        & A         & B     \\
Row 1   & 3.22222   & 5.66666   \\
Row 2   & 1.44444   & 9.99999   \\
\end{tabular}

For instance, I would like three decimal places to be printed in row 1, and one decimal place in row 2.

Is there a way to adjust the rounding precision from row 1 to row 2 as well as the number of decimal places to be printed?

Answer 1

This answer describes a way to define a common style for single rows in a tabular environment. Starting from that, I defined a command to set the precision for a single row:

• The columntype P (for: precision) is needed as a first "column". It sets the precision back to the default value at the start of every row.
• The columntype ^ has to be put before every column where this precision shall be applied. It calls \sisetup in every cell of these columns.
• Then, the macro \rowprecision can be used at the start of a tabular row to set the precision to the value given as single argument.

Your example:

\documentclass{article}

\usepackage{siunitx}
\usepackage{xifthen}
\sisetup{round-mode      = places,
         round-precision = 3,
         group-separator = {,}}
\usepackage{array}
\newcolumntype{P}{>{\global\let\currentprecision\relax}}
\newcolumntype{^}{>{\ifthenelse{\isequivalentto{\currentprecision}{\relax}}{}{\currentprecision}}}
\newcommand{\rowprecision}[1]{\gdef\currentprecision{\sisetup{round-precision=#1}}}

\begin{document}

\begin{tabular}{Pl*{2}{^S}}
    & A & B \\
    \rowprecision{4} Row 1 & 3.22222 & 5.66666   \\
    \rowprecision{2} Row 2 & 1.44444 & 9.99999   \\
\end{tabular}

\end{document}