Adjusting vertical space in tables with brackets, braces or other delimiters

Question

This question is based on a problem that arises in a solution to Inserting a small vertical space in a table.

The spacing between rows in a table is often too small. A good way to fix this is using invisible struts, as in this answer based on "Correct spacing for tables and arrays" in TeX and TUG News 1993 (Vol. 2, No. 3) by Claudio Beccari.

You define some struts and put them at the start or end of entries in the table:

\newcommand\T{\rule{0pt}{2.6ex}}       % Top strut
\newcommand\B{\rule[-1.2ex]{0pt}{0pt}} % Bottom strut

In the case of \frac, the article puts these struts in the numerator and denominator of the fraction.

But sometimes there are delimiters that automatically change size and will get larger if that strut is inserted inside them, which just leaves the same problem. Here's an example:

\documentclass{standalone}
\usepackage{amsmath}

\newcommand\T{\rule{0pt}{2.6ex}}  
\newcommand\B{\rule[-1.2ex]{0pt}{0pt}}

\begin{document}

\begin{tabular}{c|c}
\hline
row 1 & $\left(\displaystyle{\frac{1}{2}} +x\right) y$\\
\hline
row 2 & $\begin{cases} 1 & x>0\\
                                    0 & x<0\\
                                    0.5 & x=0
\end{cases}$
\\
\hline
row 3 & $\displaystyle{\binom{2}{4}}$\\
\hline
\end{tabular}
\quad
\begin{tabular}{c|c}
\hline
row 1 & $\left(\displaystyle{\frac{\T{}1}{2\B{}}} +x\right) y$\\
\hline
row 2 & $\begin{cases} \T{}1 & x>0\\
                                    0 & x<0\\
                                    0.5 & x=0\B{}
\end{cases}$
\\
\hline
row 3 & $\displaystyle{\binom{\T{}2}{4\B{}}}$\\
\hline
\end{tabular}
\quad
\begin{tabular}{c|c}
\hline
row 1 & \T{}$\left(\displaystyle{\frac{1}{2}} +x\right) y$\B{}\\
\hline
row 2 & \T{}$\begin{cases} 1 & x>0\\
                                    0 & x<0\\
                                    0.5 & x=0
\end{cases}$\B{}
\\
\hline
row 3 & \T{}$\displaystyle{\binom{2}{4}}$\B{}\\
\hline
\end{tabular}
\end{document}

and the output:

The left table is the original without struts. The middle shows the struts inside the delimiters. The right shows the struts outside the delimiters.

Any suggestions on how to fix this? [And any idea why it seems to behave okay for \binom?]

Answer 1

It is much simpler to load the cellspace package, which ensures a minimal vertical spacing for cells in columns with specifier prefixed by the letter S (or C if you load siunitx). B.t.w. for display style fractions of binomial coefficients, you have the amsmath commands \dfrac and \dbinom:

\documentclass[border=5pt]{standalone}
\usepackage{amsmath}
\usepackage{cellspace}
\setlength{\cellspacetoplimit}{4pt}
\setlength{\cellspacebottomlimit}{4pt}

\begin{document}

\begin{tabular}{c|Sc}
\hline
row 1 & $\left(\dfrac{1}{2} +x\right) y$\\
\hline
row 2 & $\begin{cases} 1 & x>0\\
                                    0 & x<0\\
                                    0.5 & x=0
\end{cases}$
\\
\hline
row 3 & $ \dbinom{2}{4}$\\
\hline
\end{tabular}

\end{document}