[Tex/LaTex] Modify arraystretch for a single row in table

spacingtables

I need to display fractions within a table and it requires to set

\renewcommand{\arraystretch}{2.3}

The problem is that not all rows contain fractions, and in this cases the white space below and above is too big. I can tweak it manually with something like \\[-2ex]. This works for the middle cases, though its a little inconvenient, but I have no idea how to reduce the absolute top space.

Something like 

\vspace{-2ex}

has no effect.

The best would be to be able to change the arraystretch for a single table row, but the command has no effect after \begin{tabular}. How can I solve this issue?

enter image description here

MWE

\documentclass{article}

\usepackage{amsmath}
\usepackage{booktabs}

\begin{document}

\begin{table}
    \renewcommand{\arraystretch}{2.3}

    \begin{tabular}{@{}c|l@{}}
            \bfseries $R_x$ & Symbol\\
            \hline\hline
            $\dfrac{a}{b}$ & $ \dfrac{A}{B} $\\
            $\dfrac{a}{b}$ & $ \dfrac{A}{B} $\\
            $\dfrac{a}{b}$ & $ \dfrac{A}{B} $\\
            \hline
    \end{tabular}
\end{table}

\end{document}

MWE with siunitx

\documentclass{article}

\usepackage{amsmath}
\usepackage{booktabs}
%\usepackage{siunitx}
\usepackage{wrapfig}

\usepackage{cellspace}
\setlength\cellspacetoplimit{4pt}
\setlength\cellspacebottomlimit{4pt}

\begin{document}

\begin{wrapfigure}[14]{R}{8.5cm}
    \renewcommand{\arraystretch}{2.3}

    \begin{tabular}{@{}Sc|Sl@{}}
            \bfseries $R_x$ & Symbol\\
            \hline\hline
            $\dfrac{a}{b}$ & $ \dfrac{A}{B} $\\
            some text & some other text \\
            $\dfrac{a}{b}$ & $ \dfrac{A}{B} $\\
            $\dfrac{a}{b}$ & $ \dfrac{A}{B} $\\
            \hline
    \end{tabular}
\end{wrapfigure}

\end{document}

Best Answer

The best solution is to use the cellspace package: it defines an adjustable minimal vertical padding around a cell. For this, you have to prefix the column specifier with the letter S (or C if you load siunitx).

With \arraystretch, there are two drawbacks: first the cell contents is no more vertically centred, and second, you have to determine, by trial and error, the stretch value – any modification of the contents may result in a new value, as is demonstrated in the following, where I modified one fraction, keeping the value you gave:

\documentclass{article}

\usepackage{amsmath}
\usepackage{booktabs, cellspace, hhline}
\setlength\cellspacetoplimit{4pt}
\setlength\cellspacebottomlimit{4pt}

\begin{document}

\begin{table}
  \renewcommand{\arraystretch}{2.3}
  \begin{tabular}{@{}c|l@{}}
    \bfseries $R_x$ & Symbol \\
    \hline\hline
    $\dfrac{a}{b}$ & $ \dfrac{A}{B} $ \\
    \hline
    $\dfrac{a}{b}$ & $ \dfrac{A}{B + \cfrac{C}{D}} $ \\
    \hline
    $\dfrac{a}{b}$ & $ \dfrac{A}{B} $ \\
    \hline
  \end{tabular}
\hskip2cm
  \begin{tabular}{@{}Sc|Sl@{}}
    \bfseries $R_x$ & Symbol \\
    \hline\hline
    $\dfrac{a}{b}$ & $ \dfrac{A}{B} $ \\
    \hline
    $\dfrac{a}{b}$ & $ \dfrac{A}{B + \cfrac{C}{D}} $ \\
    \hline
    $\dfrac{a}{b}$ & $ \dfrac{A}{B} $ \\
    \hline
  \end{tabular}
\end{table}
\end{document}

rendered document

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