How can I lay out multiple choice answers as a matrix with exam?

Question

For creating a test I use the exam class, which worked out fine so far. Now I need to implement a question with the possible answers beeing a matrix like this:

However I can't manage to put the \choice command (of the exam class) in that form (I want to use exam for printing automatic solution papers also). When I simply put it inside a tabular it does not seem to work out. How could I realize this?

PS: The example above (just as a visual explanation, it is not using the exam class) is:

\documentclass{exam}
\usepackage{amssymb} 
\begin{document}
    \renewcommand{\arraystretch}{1.4}
    \begin{tabular}{r|ccc}
     & Orange & Green & Aubergine \\
     \hline
     Fruit & $\Box$ & $\Box$ & $\Box$ \\
     Vegetable & $\Box$ & $\Box$ & $\Box$ \\
     Colorname & $\Box$ & $\Box$ & $\Box$ \\
    \end{tabular}\
\end{document}

[Edit: add example code] [Edit2: Clarify question]

Answer 1

The exam documentation states:

The checkboxes environment creates a list environment with the choices as the items in the list.

So every \begin{checkboxes}...\end{checkboxes} creates a new list. You can't put different items from the same list in different cells in a table. So you'll need to create a new one-item list for every cell in your table. And you can't put a list in a tabular without having a predefined column width. So either use alignment options (p, m, b, ...) that give you a fixed column width or put the list in a minipage-like environment such as varwidth (which will also horizontally center its content).

As our lists are one-item lists and we don't really want them to look like a list, we'll need some customization. In the exam class this is done width \checkboxeshook. So go for:

\renewcommand{\checkboxeshook}{
    \setlength{\labelwidth}{0pt}
    \setlength{\labelsep}{0pt}
    \setlength{\leftmargin}{0pt}
}

Now make a macro so you don't need to copy paste too much code. This will also increase the readability of your code. Here are 2 macros. One for a regular checkbox option and one for the correct choice checkbox:

\newcommand{\tablechoice}{\begin{varwidth}{\textwidth}\begin{checkboxes}\choice\end{checkboxes}\end{varwidth}}
\newcommand{\tablecorrectchoice}{\begin{varwidth}{\textwidth}\begin{checkboxes}\CorrectChoice\ \end{checkboxes}\end{varwidth}}

All these things put together get you:

\documentclass[answers]{exam}
\usepackage{amssymb}
\usepackage{varwidth}

\renewcommand{\arraystretch}{1.4}

\newcommand{\tablechoice}{\begin{varwidth}{\textwidth}\begin{checkboxes}\choice\end{checkboxes}\end{varwidth}}
\newcommand{\tablecorrectchoice}{\begin{varwidth}{\textwidth}\begin{checkboxes}\CorrectChoice\ \end{checkboxes}\end{varwidth}}

\checkboxchar{$\Box$}
\checkedchar{$\blacksquare$}

\renewcommand{\checkboxeshook}{
    \setlength{\labelwidth}{0pt}
    \setlength{\labelsep}{0pt}
    \setlength{\leftmargin}{0pt}
}

\begin{document}

\begin{questions}

    \question Answer the following question: \\
    \begin{tabular}{r|*3{c}}
        & Orange & Green & Aubergine \\ \hline
        Fruit & \tablechoice & \tablechoice & \tablechoice \\
        Vegetable & \tablechoice & \tablecorrectchoice & \tablechoice \\
        Colorname & \tablechoice & \tablechoice & \tablechoice \\
    \end{tabular}

\end{questions}

\end{document}

Answer 2

Based on Maarten Dhondt's helpful answer I built myself an environment with the number of horizontal options to avoid repeating myself for other questions:

\documentclass[answers]{exam}
\usepackage{amssymb}
\usepackage{varwidth}

\newenvironment {choicetable} [1] {
    \renewcommand{\arraystretch}{1.7}
    \renewcommand{\checkboxeshook}{
        \setlength{\labelwidth}{0pt}
        \setlength{\labelsep}{0pt}
        \setlength{\leftmargin}{0pt}
    }
    \newcommand{\CO}{\begin{varwidth}{\textwidth}\begin{checkboxes}\choice\end{checkboxes}\end{varwidth}}
    \newcommand{\CX}{\begin{varwidth}{\textwidth}\begin{checkboxes}\CorrectChoice\ \end{checkboxes}\end{varwidth}}
    \begin{tabular}{r*{#1}{c}}
} {
    \end{tabular}   
}
\checkboxchar{$\Box$}
\checkedchar{$\blacksquare$}


\begin{document}
\begin{questions}
    \question Answer the following question: \\
    \begin{choicetable}{3}
        & Orange & Green & Aubergine \\ \hline
        Fruit & \CO & \CO & \CO \\
        Vegetable & \CO & \CX & \CO \\
        Colorname & \CO & \CO & \CO \\
    \end{choicetable} 
\end{questions}
\end{document}

Answer 3

Something like this?

\documentclass[11p,twoside,a4paper,leqno]{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{fourier}
\usepackage{mathtools}
\usepackage{amsfonts}
\usepackage[x11names]{xcolor}
\usepackage{array, makecell, eqparbox}
\newcommand\tsq{$\square$}
\newcommand\colhead[2][black]{\eqmakebox[H][c]{\color{#1}{#2}}}
\setcellgapes{8pt}

\begin{document}
\begin{center}
  \makegapedcells
  \begin{tabular}{@{}r! {\vrule width 0.8pt}*{3}{c}}%{>{\centering $}m{2cm}<{$}}
                & \colhead[DarkOrange3]{Orange} & \colhead[OliveDrab3]{Green} & \colhead[Plum4]{Aubergine} \\
    \Xhline{0.8pt}
    Fruit & \tsq & \tsq & \tsq \\
    Vegetable & \tsq & \tsq & \tsq \\
    Colour name & \tsq & \tsq & \tsq
  \end{tabular}
\end{center}

\end{document}