Arraystretch in tabular environment produces misalignment

Question

The following code

\documentclass[12pt,a4paper]{article}
\usepackage{array}
\usepackage{calc}
\begin{document}
\newcolumntype{L}[1]{>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}

\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}} r L{\textwidth * \real{0.8}}} 
\hline
Languages & Italian (native tongue), English (very fluent), German (beginner). \\
\hline
Chats & bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla  \\
\hline
Programming & C, Java, OCaml, Bash, Fortran. Currently learning Python and R. \\
\hline
\end{tabular*}
\end{document}

produces this:

If I add

\renewcommand{\arraystretch}{4}

before the tabular code, the output is this:

If, additionally, I change the definition of L using the p column as follows

\newcolumntype{L}[1]{>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}p{#1}}

then I get this:

None of these is the output I want. I would like every cell to be vertically centered. Why does this happen? How can I fix it? I tried to use different solutions (such as \setlength{\extrarowheight}{4pt}), but all of them are affected by the same problem.

Answer 1

You're using the wrong tool:

\documentclass[12pt,a4paper]{article}
\usepackage{tabularx,booktabs}

\setlength{\heavyrulewidth}{\lightrulewidth}
\setlength{\aboverulesep}{12pt}% choose
\setlength{\belowrulesep}{12pt}% choose

\begin{document}

\noindent
\begin{tabularx}{\textwidth}{@{} r X @{}}
\toprule
Languages & Italian (native tongue), English (very fluent), German (beginner). \\
\midrule
Chats & bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
        bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
        bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
        bla bla bla bla bla bla bla bla bla bla bla bla bla bla  \\
\midrule
Programming & C, Java, OCaml, Bash, Fortran. Currently learning Python and R. \\
\bottomrule
\end{tabularx}

\end{document}

If you want the label vertically centered with respect to the body (but I wouldn't do it), you can set the type of the X column to m:

\documentclass[12pt,a4paper]{article}
\usepackage{tabularx,booktabs,array}

\setlength{\heavyrulewidth}{\lightrulewidth}
\setlength{\aboverulesep}{12pt}% choose
\setlength{\belowrulesep}{12pt}% choose
\renewcommand{\tabularxcolumn}[1]{m{#1}}

\begin{document}

\noindent
\begin{tabularx}{\textwidth}{@{} r X @{}}
\toprule
Languages & Italian (native tongue), English (very fluent), German (beginner). \\
\midrule
Chats & bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla 
        bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla 
        bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla 
        bla bla bla bla bla bla bla bla bla bla bla bla bla bla  \\
\midrule
Programming & C, Java, OCaml, Bash, Fortran. Currently learning Python and R. \\
\bottomrule
\end{tabularx}

\end{document}

Answer 2

Issues with m column types is explained in David Carlisle answer. Unfortunately use of \arraystreatch and column type p doesn't gives equal vertical space between hlines and cells contents. Solution seems to be not use \arraystreatch and desired vertical space obtain on different way, for example with rules provided by package booktabs:

Eddit: For vertical centering of a text in the first column, you should add

\renewcommand\tabularxcolumn[1]{m{#1}}

with detewrminatin veritical space as used egreg in his answer the MWE is:

\documentclass{article}
\usepackage{booktabs,tabularx}
\renewcommand\tabularxcolumn[1]{m{#1}}
\newcolumntype{L}{>{\raggedright\let\newline\\\arraybackslash}X}
\setlength{\aboverulesep}{2ex}% choose
\setlength{\belowrulesep}{2ex}% choose

\usepackage[active,floats,tightpage]{preview}
\setlength\PreviewBorder{2ex}

\begin{document}
\begin{table}[htb]% <-- added for preview
\begin{tabularx}{\textwidth}{rX}
    \midrule
Languages & Italian (native tongue), English (very fluent), German (beginner). \\
    \midrule
Chats & bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla  \\
    \midrule
\end{tabularx}
\end{table}
\end{document}

In above MWE instead tabular the tabularx environment is used. It gives equal column width as your (wrongly) used determination of the space between columns.

Answer 3

an m column type places the reference point in the vertical centre of its content without considering the internal baselines. so any alignment of text in an m column to text in surrounding columns is essentially accidental. (If you narrow the column slightly so that the text breaks over two lines, then it will re-align in this case)

p or b columns do set the reference point to an internal baseline (top or bottom line, respectively) and with p you get alignment again as shown below.

\documentclass[a4paper]{article}
\addtolength\textwidth{2cm}
\usepackage{array}
\renewcommand{\arraystretch}{4}
\begin{document}

\newcolumntype{L}[1]{%
>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}

\centering
\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}} r L{0.8\textwidth}}
\hline
Languages & Italian (native tongue), English (very fluent), German (beginner). \\
\hline
Programming & C, Java, OCaml, Bash, Fortran. Currently learning Python and R. \\
\end{tabular*}

\newcolumntype{L}[1]{%
>{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}p{#1}}

\centering
\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}} r L{0.8\textwidth}}
\hline
Languages & Italian (native tongue), English (very fluent), German (beginner). \\
\hline
Programming & C, Java, OCaml, Bash, Fortran. Currently learning Python and R. \\
\end{tabular*}

\end{document}