Creating a Matrixlist package

Question

I haven't been able to find a suitable package that does what I want. The closest is parcolumns and I've spent several hours trying to understand TeX programming and the parcolumns style. While I got the most of it I've tried to tweak it and just can't get it to do what I want.

I'm curious if anyone either knows of a package or can write one up quickly that does the following:

1. You give it a \\ terminated list just like enumerate and the number of columns;

2. It internally groups the list by number of columns. (a,b,c,d,e) with columns=2 will be grouped as ((a,b,c),(d,e));

3. It then creates m rows (\hboxes, depending on the number of elements and column size). The nth row contains an \hbox of the nth element in each group. This creates a matrix

   a d
   b e
   c

4. Each element in the row tries to distribute itself evenly along the horizontal BUT if on element overlaps the next it will "push" it INSTEAD of overlapping it (and this will continue until there is no need to push);

5. No gaps between rows AND no end gap on last column (so one has to get the width of the largest element in the last column and set the column size to that).

The point here is we have a matrix of boxes BUT if the horizontal content of one box is larger than the space it is given it will simply shift the adjacent box over to make room for it BUT if not it will align in a distributed manner.

Hopefully that makes sense and there is already a package that does this. With parcolumns I have two issues: When my elements are horizontally too large (even if just a little) they overlap the next column and I have to manually push that next element over (which may cause a chain reaction).

---

\documentclass{article}
\usepackage{tikz}
\scrollmode


\begin{document}

\newcommand{\drawrect}[1]{\fbox{\begin{tikzpicture} \fill (-#1,-1) rectangle (#1,1);\end{tikzpicture}}}

\noindent\fbox{\hbox to \linewidth{%
\drawrect{1.5}\hspace*{\fill}\drawrect{1.5}\hspace*{\fill}\drawrect{1.5}\\}}
\fbox{\hbox to \linewidth{\drawrect{2}\hspace{0.2cm}\drawrect{1.5}\hspace{1.2cm}\drawrect{1.5}\\}}
\fbox{\hbox to \linewidth{\drawrect{2.5}\hspace{0.2cm}\drawrect{1.5}\hspace{0.2cm}\drawrect{1.5}\\}}
\fbox{\hbox to \linewidth{\drawrect{2.4}\hspace{0.4cm}\drawrect{1.5}\hspace{0.2cm}\drawrect{1.5}\\}}

\end{document}

Here is an example situation

1. Note that the first element of row 3 "pushes" or overlaps into the 2nd element of row.
2. This causes the 2nd element to be offset by some amount (user specified). The 3rd element does not change positions though.
3. In row 4, the first element is slightly smaller BUT note that the 2nd element is aligned with the one right above it BECAUSE it snaps to that position to for visual reasons.
4. Also, if you were to add a fixed amount of whitespace to each element in the last column then you would end up causing problems (depends on how you set it up though). I want to remove this issue. To fix it we basically have to remove the whitespace so that at least one element in the last column has no whitespace. Hence we just "substract" the appropriate amount of whitespace from all columns and then at least one will have no whitespace. Note that this is only for calculating the column spacing. Essentially we just compute (\linewidth + x)/#columns where x is the smallest amount of whitespace from the set of cells in the last column. This effectively increases the \linewidth by the unused whitespace in the last column.

Answer 1

Well,... visually aligning boxes depending on rows above and below isn't really the tex way (not impossible, but....) I'd go for a layout like this, where the entries are just equally spaced in the rows.

To get each of the boxes (or if you want, just the boxes in the last column) to be natural width rather than a specified width of short, use \begin{minipage}{\xxx} for fixed boxes and \begin{varwidth}{\xxx} for the boxes on at least the last column where \xxx is textwidth divided by number of columns, adjusting for any space or rules between columns. varwidth from the package of the same name is like minipage but sets the box to a narrower width of possible.

If you use varwidth in the last column, the entire construct will not be full width, but can just be centered (with \centering in that case) as I think you wanted.

If that layout is acceptable, the other syntactic issues, like calculating column width and entering cells in column major rather than row major order can be sorted if need be.

\documentclass{article}
\usepackage{tikz}
\scrollmode


\begin{document}

\noindent X\dotfill X

\noindent X\dotfill X

\newcommand{\drawrect}[1]{\fbox{\begin{tikzpicture} \fill (-#1,-1) rectangle (#1,1);\end{tikzpicture}}}

\def\onerow#1{\par\noindent\fbox{%
  \dimen0=\textwidth
  \advance\dimen0-2\fboxsep
  \advance\dimen0-2\fboxrule
\hbox to \dimen0{#1}}}


\onerow{\drawrect{1.5}\hfill\drawrect{1.5}\hfill\drawrect{1.5}}
\onerow{\drawrect{2}\hfill\drawrect{1.5}\hfill\drawrect{1.5}}
\onerow{\drawrect{2.5}\hfill\drawrect{1.5}\hspace{0.2cm}\drawrect{1.5}}
\onerow{\drawrect{2.4}\hfill\drawrect{1.5}\hspace{0.2cm}\drawrect{1.5}}

\end{document}