Specifying minimal (not fixed) width in tabular

Question

I want some columns in my tables to have a minimal column width, that should always be maintained, even if the content is smaller, but increased when the content is wider.

Bounty-related update: @Sandy G's answer produces the desired behavior, but I want it to be a column type so that I can specify it like this:

\documentclass{article}
\begin{document}
  \begin{tabular}{m{2cm}m{2cm}m{1cm}m{1cm}}
    Longer entry here&2&3&4\\
    5&6&Longer entry here&8
  \end{tabular}
\end{document}

Answer 1

See ADDENDUM and BONUS

First, the original approach.

Here is a \newcolumntype solution, except that, for a reason that I should know but I don't, it won't work in the last column of the tabular. I'm sure David C. could tell me off the cuff why.

So I've provided C{}, L{}, and R{} column types for specifying a minimum width, and an Q column type to use for a phantom, to get around the deficiency I initially cited.

\documentclass{article}
\usepackage{tabularx,stackengine}
\newcolumntype{L}[1]{>{\minwd l{#1}}l<{\endminwd}}
\newcolumntype{C}[1]{>{\minwd c{#1}}c<{\endminwd}}
\newcolumntype{R}[1]{>{\minwd r{#1}}r<{\endminwd}}
\def\minwd#1#2#3\endminwd{\stackengine{0pt}{#3}{\rule{#2}{0pt}}{O}{#1}{F}{F}{L}}
\newcolumntype{Q}{@{}c@{}}
\begin{document}
\begin{tabular}{|C{1.2cm}|C{1.2cm}|R{2cm}|l|}
a & a& b& c\\
aaaaaaaaaaaaaaaaa& aa& bb& cc\\
\end{tabular}
\bigskip


\begin{tabular}{|C{1.2cm}|C{1.2cm}|R{2cm}|L{1.5cm}|Q}
a & a& b& c&\\
aaaaaaaaaaaaaaaaa& aa& bb& cc&\\
\end{tabular}
\end{document}

---

ADDENDUM

Apparently the way to overcome the deficiency I noted in my original solution is to use \collectcell:

\documentclass{article}
\usepackage{tabularx,stackengine,collcell}
\let\endminwd\relax
\newcolumntype{L}[1]{>{\collectcell\xminwd l{#1}}l<{\endminwd\endcollectcell}}
\newcolumntype{C}[1]{>{\collectcell\xminwd c{#1}}c<{\endminwd\endcollectcell}}
\newcolumntype{R}[1]{>{\collectcell\xminwd r{#1}}r<{\endminwd\endcollectcell}}
\def\minwd#1#2#3\endminwd{\stackengine{0pt}{#3}{\rule{#2}{0pt}}{O}{#1}{F}{F}{L}}
\newcommand\xminwd[1]{\minwd#1}
\begin{document}
\begin{tabular}{|C{1.2cm}|C{1.2cm}|R{2cm}|L{1.5cm}|}
a & a& b& c\\
aaaaaaaaaaaaaaaaa& aa& bb& cc\\
\end{tabular}
\end{document}

And just for fun, if you set the vertical measure of the \rule to something nonzero, say 1pt, you can see how the rule comes into play:

---

BONUS

I realized the technique could be used for creating a D column for aligning a specified number of trailing decimal places. EDITED to handle decimal free inputs.

\documentclass{article}
\usepackage{tabularx,stackengine,collcell}
\let\endecm\relax
\newcolumntype{D}[1]{>{\collectcell\Decm l{#1}}r<{..\endDecm\endcollectcell}}
\def\decm#1#2#3.#4.#5\endDecm{#3.\stackengine{0pt}{#4}{\rule{#2\wd0}{0pt}}{O}{#1}{F}{F}{L}}
\newcommand\Decm[1]{\setbox0=\hbox{0}\decm#1}
\begin{document}
\begin{tabular}{|D{3}|D{2}|D{4}|}
10.345 & 410.34 & 1310.34\\
10 & 11 & 12.\\
210.34 & 1210.3 & 310.3456\\
\end{tabular}
\end{document}

Answer 2

This could be done by placing a row of 0pt \rules with a negative row separator (for proper vertical alignment).

In the example, columns 1 and 2 have minimum width 2cm, while columns 3 and 4 have minimum width 1cm.

\documentclass{article}

\begin{document}
\[
\begin{tabular}{cccc}
\rule{2cm}{0pt}&\rule{2cm}{0pt}&\rule{1cm}{0pt}&\rule{1cm}{0pt}\\[-\arraystretch\normalbaselineskip]]
Longer entry here&2&3&4\\
5&6&Longer entry here&8
\end{tabular}
\]
\end{document}

Update: By placing the \rule in a macro, you can adjust the fixed minimum in the document body similarly to a column type.

Here is the code:

\documentclass{article}

\newcommand{\fixedmin}[1]{\rule{#1}{0pt}&\rule{#1}{0pt}&\rule{#1}{0pt}&\rule{#1}{0pt}\\[-\arraystretch\normalbaselineskip]}

\begin{document}

\noindent Here is a table with fixed minimum width 2 cm.
\[
\begin{tabular}{cccc}\fixedmin{2cm}
Longer entry here&2&3&4\\
5&6&Longer entry here&8
\end{tabular}
\]

\noindent Here is a table with fixed minimum width 1 cm.
\[
\begin{tabular}{cccc}\fixedmin{1cm}
Longer entry here&2&3&4\\
5&6&Longer entry here&8
\end{tabular}
\]

\noindent Here is a table with no fixed minimum width.
\[
\begin{tabular}{cccc}
Longer entry here&2&3&4\\
5&6&Longer entry here&8
\end{tabular}
\]

\end{document}

Answer 3

Here's a way to do it using the collcell package. The idea is to measure the content of the cell and then add rules to make up the deficit where appropriate. I've made versions for c, r and l columns. The vertical lines are just there to show the fixed width columns.

\documentclass{article}
\usepackage{array,calc,collcell}
\newlength{\fwlen}
\newcolumntype{C}[1]{>{\setlength{\fwlen}{#1}\collectcell\fixedCwidth}c<{\endcollectcell}}
\newcolumntype{R}[1]{>{\setlength{\fwlen}{#1}\collectcell\fixedRwidth}r<{\endcollectcell}}
\newcolumntype{L}[1]{>{\setlength{\fwlen}{#1}\collectcell\fixedLwidth}l<{\endcollectcell}}
\makeatletter
\newcommand{\fixedCwidth}[1]{\setlength{\@tempdima}{\widthof{#1}}\ifdim\@tempdima>\fwlen #1\else\setlength{\@tempdimb}{(\fwlen-\@tempdima)/2}\rule{\@tempdimb}{0pt}#1\rule{\@tempdimb}{0pt}\fi}
\newcommand{\fixedLwidth}[1]{\setlength{\@tempdima}{\widthof{#1}}\ifdim\@tempdima>\fwlen #1\else\setlength{\@tempdimb}{\fwlen-\@tempdima}#1\rule{\@tempdimb}{0pt}\fi}
\newcommand{\fixedRwidth}[1]{\setlength{\@tempdima}{\widthof{#1}}\ifdim\@tempdima>\fwlen #1\else\setlength{\@tempdimb}{\fwlen-\@tempdima}\rule{\@tempdimb}{0pt}#1\fi}
\makeatother
\begin{document}


\begin{tabular}{|C{1cm}|L{1cm}|R{1cm}|C{1cm}|C{1cm}|}
123 &   123 &   123 &   123 & This is a wider column\\
5   &   6   &   6   &   8 & 8
\end{tabular}

\end{document}

Answer 4

To do it properly, you need a minimum width and a maximum width of each column. You required the minimum width in your question. I'd say, it is better to have a maximum width, because otherwise your tabular might run out of the margin.

\documentclass{article}
\usepackage{array} 
\usepackage{varwidth}% varwidth defines a new column type V.

\begin{document}
\begin{tabular}{*{4}{V{4cm}}}
\hspace*{2cm} & \hspace*{2cm} & \hspace*{1cm} & \hspace*{1cm}\\[-1em]
    Longer entry here&2&3&4\\
    5&6&Longer entry here, which gets wrapped finaly&8\\
  \end{tabular}
\end{document}

There are two small tricks.

First, the varwidth package defines a new column type, but this is not documented in the manual, I found it here: https://texfaq.org/FAQ-varwidcol

V{4cm}sets the maximum width of a column.

Second: we need a minimum width. We just can take an empty line of the tabular and fill it with empty spaces of the needed minimum width. To hide this line, I inserted \\[-1em], which you need to adapt in your use case. I suggest to put it as first line of the tabular, followed by the head of the tabular, not the other way round.

Hopefully it works in your use case!