[Tex/LaTex] Remove list margin only inside table

enumitemitemizepandoc

I'm trying to style itemize lists that appear in tabular environments (specifically in a longtable). Ideally, I'd like to remove the left margin from lists that appear in tables while maintaining the margin on lists outside of tables.

There are several answers here already about how to use the enumitem package to change the margins of lists: you can set leftmargin=* on specific lists, or you can create a new custom itemize environment and use it specifically inside tables.

However, I am using pandoc to convert Markdown into TeX, so I have no control over the resulting TeX output—I can't add \begin{itemize}[leftmargin=*] or use a custom \begin{marginlessitemize}. enumitem has a \setlist macro that lets you set list settings globally, and \setlist[itemize]{leftmargin=*} removes the left margin from all lists, which isn't ideal, since I'm only trying to target lists inside tables.

Is there a way to apply \setlist{...} only to itemize environments that are nested inside tabular environments? In a perfect world, it'd be cool to use some sort of logic in the preamble: if itemize is in a table, use no margin; otherwise use a margin.

Here's a MWE…

(The messy longtable output comes from this Markdown table, which pandoc converts into TeX):

+-----------+-----------+
| Thing     | List      |
+===========+===========+
| Thing 1   | - Item 1  |
|           | - Item 2  |
+-----------+-----------+
| Thing 2   | - Item 3  |
|           | - Item 4  |
+-----------+-----------+

This TeX file…

\documentclass[11pt,article,oneside]{memoir}

\usepackage{longtable}

\begin{document}

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

\begin{itemize}
\tightlist
\item
  Item 1
\item
  Item 2
\end{itemize}

\begin{longtable}[]{@{}ll@{}}
\caption{This is a table.}\tabularnewline
\toprule
\begin{minipage}[b]{0.21\columnwidth}\raggedright
Thing
\end{minipage} & \begin{minipage}[b]{0.27\columnwidth}\raggedright
List
\end{minipage}\tabularnewline
\midrule
\endfirsthead
\toprule
\begin{minipage}[b]{0.21\columnwidth}\raggedright
Thing
\end{minipage} & \begin{minipage}[b]{0.27\columnwidth}\raggedright
List
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.21\columnwidth}\raggedright
Thing 1
\end{minipage} & \begin{minipage}[t]{0.27\columnwidth}\raggedright
\begin{itemize}
\tightlist
\item
  Item 1
\item
  Item 2
\end{itemize}
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.21\columnwidth}\raggedright
Thing 2
\end{minipage} & \begin{minipage}[t]{0.27\columnwidth}\raggedright
\begin{itemize}
\tightlist
\item
  Item 3
\item
  Item 4
\end{itemize}
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

\end{document}

…generates this PDF:

Margins in and out of the table

If I add this to the preamble…

\usepackage{enumitem}
\setlist[itemize]{leftmargin=*}

…the left margin in the list inside the table disappears, but it also disappears in the list outside the table:

No margins anywhere

If I create a custom itemize environment, I can use it in the table:

\newlist{marginlessitemize}{itemize}{1}
\setlist[marginlessitemize]{label=\textbullet,leftmargin=*}

...

% Inside a table cell...
\begin{marginlessitemize}
\item
  Item 1
\item
  Item 2
\end{marginlessitemize}

No margin in, yes margin out

That works, but because the TeX is generated automatically, I can't use the custom environment without manually editing the converted file. Hence the need to somehow automatically set no margin on lists inside tables.

Best Answer

The following works (just for longtable) if you place it in your preamble:

\makeatletter
\let\LT@arraybak\LT@array
\def\LT@array{\setlist[itemize]{leftmargin=*,after=\strut}\LT@arraybak}
\makeatother

Complete MWE:

\documentclass[11pt,article,oneside]{memoir}

\usepackage{longtable}
\usepackage{enumitem}
\makeatletter
\let\LT@arraybak\LT@array
\def\LT@array{\setlist[itemize]{leftmargin=*,after=\strut}\LT@arraybak}
\makeatother



\begin{document}

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

\begin{itemize}
\tightlist
\item
  Item 1
\item
  Item 2
\end{itemize}

\begin{longtable}[]{@{}ll@{}}
\caption{This is a table.}\tabularnewline
\toprule
\begin{minipage}[b]{0.21\columnwidth}\raggedright
Thing
\end{minipage} & \begin{minipage}[b]{0.27\columnwidth}\raggedright
List
\end{minipage}\tabularnewline
\midrule
\endfirsthead
\toprule
\begin{minipage}[b]{0.21\columnwidth}\raggedright
Thing
\end{minipage} & \begin{minipage}[b]{0.27\columnwidth}\raggedright
List
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.21\columnwidth}\raggedright
Thing 1
\end{minipage} & \begin{minipage}[t]{0.27\columnwidth}\raggedright
\begin{itemize}
\tightlist
\item
  Item 1
\item
  Item 2
\end{itemize}
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.21\columnwidth}\raggedright
Thing 2
\end{minipage} & \begin{minipage}[t]{0.27\columnwidth}\raggedright
\begin{itemize}
\tightlist
\item
  Item 3
\item
  Item 4
\end{itemize}
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

\end{document}

improved spacing

For a short explanation: The start of the longtable-environment is defined as: 

macro:->\par \ifx \multicols \@undefined \else \ifnum \col@number
>\@ne \@twocolumntrue \fi \fi \if@twocolumn \LT@err {longtable not
in 1-column mode}\@ehc \fi \begingroup \@ifnextchar [\LT@array {\LT@array
[x]}

So after evaluating some stuff it calls the \LT@array macro in which we inject our code which alters the itemize-environment and because it is inside of a \begingroup...\endgroup construct the changes made are local.

EDIT: To improve the vertical spacing I added after=\strut to the \setlist.

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