Stepped table in booktabs

Question

I am looking to typeset the following table in booktabs:

I am not sure how to get the steps highlighting the differences between the units in the image. The use of \cmidrule makes the horizontal rules, but leaves quite a bit of space in between the rules. If I then add \belowrulesep=0pt \aboverulesep=0pt, the spaces around the top, mid and bottom rules get messed up. How do I get tight spacing around \cmidrule, but not elsewhere?

Also, the only answer I find about using vertical rules in booktabs is 'don't use vertical rules', which is quite right in general. Still, I think vertical rules in this specific instance are justified. So how do I get these limited vertical rules?

This is what I tried so far:

\documentclass[a4paper,12pt]{article}
\usepackage{booktabs}
\title{HGCS table}
\begin{document}
% \belowrulesep=0pt
% \aboverulesep=0pt
\begin{tabular}{lllllll}
\toprule
   & ich & machen & dorf & das & apfel & pfund \\
\midrule
1  & ik & maken & dorp & dat & appel & pund \\\cmidrule{2-2}
2  & ich & maken & dorp & dat & appel & pund \\\cmidrule{3-3}
3  & ich & machen & dorp & dat & appel & pund \\\cmidrule{4-4}
4  & ich & machen & dorf & dat & appel & pund \\\cmidrule{5-5}
5  & ich & machen & dorf & das & appel & pund \\\cmidrule{6-6}
6  & ich & machen & dorf & das & apfel & pund \\\cmidrule{7-7}
7  & ich & machen & dorf & das & apfel & pfund \\
\bottomrule
\end{tabular}%
\end{document}

Answer 1

This seems to be close to the design you want to achieve:

\documentclass[a4paper,12pt]{article}
\usepackage{booktabs}
\usepackage{array}
\title{HGCS table}
\begin{document}

\setlength\extrarowheight{2pt}
\begin{tabular}{lllllll}
\toprule
Dialects & \multicolumn{6}{c}{Lexical Items}\\\cmidrule{2-7}
   & ich & machen & dorf & das & apfel & pfund \\
\midrule
Low German\\
1  & ik & maken & dorp & dat & appel & pund \\\cline{2-2}
2  & ich & \multicolumn{1}{|l}{maken} & dorp & dat & appel & pund \\\cline{3-3}
3  & ich & machen & \multicolumn{1}{|l}{dorp} & dat & appel & pund \\\cline{4-4}
Middle German & & & & \multicolumn{1}{|l}{}\\
4  & ich & machen & dorf & \multicolumn{1}{|l}{dat} & appel & pund \\\cline{5-5}
5  & ich & machen & dorf & das & \multicolumn{1}{|l}{appel} & pund \\\cline{6-6}
6  & ich & machen & dorf & das & apfel & \multicolumn{1}{|l}{pund} \\\cline{7-7}
High German \\
7  & ich & machen & dorf & das & apfel & pfund \\
\bottomrule
\end{tabular}%
\end{document}

Instead of the rules from booktabs I have used normal \clines for the horizontal parts of the separating line. For the vertical parts, I have used the multicolumn command in order to add a | to the definition of the corresponding cells. In order to increase the vertical distance between the table rows, I have added \setlength\extrarowheight{2pt}.

Answer 2

You can do that with {NiceTabular} of nicematrix.

This environment is similar to the classical environment {tabular} (of array) but constructs also PGF/Tikz nodes under the rows, columns and cells of the array. In the \CodeAfter, it's possible to use these nodes to draw whatever rule you want.

\documentclass[a4paper,12pt]{article}
\usepackage{booktabs}
\usepackage{nicematrix,tikz}
\title{HGCS table}
\begin{document}
\begin{NiceTabular}{lllllll}
\toprule
Dialects & \Block{1-*}{Lexical items} \\
\cmidrule{2-7}
   & ich & machen & dorf & das & apfel & pfund \\
\midrule
Low German \\
1.  & ik  & maken & dorp & dat & appel & pund \\
2.  & ich & maken & dorp & dat & appel & pund \\
3.  & ich & machen & dorp & dat & appel & pund \\
Middle German \\
4.  & ich & machen & dorf & dat & appel & pund \\
5.  & ich & machen & dorf & das & appel & pund \\
6.  & ich & machen & dorf & das & apfel & pund \\
High German \\
7.  & ich & machen & dorf & das & apfel & pfund \\
\bottomrule
\CodeAfter
 \tikz \draw (5-|2) -| (6-|3) -| (7-|4) -| (9-|5) -| (10-|6) 
                    -| (11-|7) -- (11-|last) ;
\end{NiceTabular}
\end{document}