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From: C38871CF@WUVMD.BITNET ("Charles H. Franklin")
Newsgroups: comp.text.tex
Subject: Decimal Alignment in LaTeX tables
Message-ID: <425D375D00003736@Post-Office.UH.EDU>
Date: 29 Apr 91 06:27:23 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 151

Since asking about decimal alignment on Saturday I've received about a dozen
responses.  I can't believe how helpful you all are.  After trying
unsuccessfully several times in the past to get a solution to decimal
alignment, it is really nice to get so much help so fast.
 
From the comments in the replies, it seems I am not the only one who has
wanted decimal alignment. So I thought I would post a summary of the various
solutions so we can all see what the options appear to be.
 
1) Use \hphantom to add spaces where needed. eg
    \newcommand{\Z}{\hphantom{0}}
    \newcommand{\M}{\hphantom{$-$}}
then
    1.0\Z\Z    &   \M0.0003
    0.333      &   $-0.0001$
line up like you want.  {Note you can also do this for the ")" on the standard
errors in my example. This is essentially the solution I have been using.}
 
2) Use the @{.} argument in the tabular declaration to create two columns with
no spaces and a decimal point between them. eg
          \begin{tabular}{r@{.}l}
                  10&7 \\
                   1&3 \\
                   0&75
          \end{tabular}
produces
                  10.7
                   1.3
                   0.75
 
3) Use DECALIGN.STY (available from FILESERV@SHSU) which implements a "d"
alignment argument for the tabular environment. This "d" alignment type is in
fact a version of (2) above. It defines two columns with a decimal between
them and uses the decimal as the column separator, thus allowing you to write
3.14 instead of 3&14. This means that "d" is really r@{.}l, so you must
remember that it is in fact two columns instead of one, important when making
the headings for the column.
 
4) Follow the lead of REVTEX and define \dec x.xx which produces a box of
equal width on both sides of the decimal place. When used with a center
aligned column, this produces decimal alignment. To see the REVTEX code, scan
REVTEX.STY for the string "\dec". (Or see below.)
 
 
OK, those are the proposed solutions. Each will work. Obviously preferences
over these is partly subjective and I guess they depend on what you are used
to. But here are my own thoughts on the solutions, and a solution of my own.
 
1) The \hphantom space is what I've been doing. It suffers from having to
think too much in constructing tables, and more so from the problem of what to
do when you have too much, rather than too little, after the decimal. For
example, if an asterisk is used to indicate a statistically significant
coefficient, eg    2.227* then the problem with alignment is the asterisk
takes up too much space. Fixing this using phantom space is possible but
painful.
 
2) and 3)  The r@{.}l solution is attractive because it is built in to LaTeX.
The DECALIGN style is really the same thing but makes "d" do what r@{.}l does,
plus a little more. Either of these is workable. My objection is the fact that
this produces two columns masquerading as only one. I'm sure those who use
this solution quickly get used to it, but I think a column should be a column
and not two. With DECALIGN this is especially inconsistent, since "d" looks
just like "r" or "l" but it behaves quite differently.   This caused me
trouble when I tried DECALIGN on a table I had in a paper. The table used
blank cells for some coefficients which where estimated in one column but not
in others. This gave DECALIGN fits. Presumably because my one column of blank
cells was now only half of the expected two columns. Certainly I could fix it,
but I don't like that kind of inconsistency. I also don't like 3&14 in place
of 3.14, (though this can be avoided with DECALIGN), because it seems more
error prone.
 
4) \dec x.xx has the major drawback that you have to enter it for every cell
you want aligned on the decimal. A global declaration would be much nicer.
 
In the end, I've settled on 4) as the less worse solution. A "d" alignment
primitive in LaTeX is the obvious "right" solution, but is not available.
For me, I think the "two-columns-in-one" solution of 2) and 3) is just too
inconsistent with the rest of the information in the table. So I've opted for
the \dec x.xx solution, even though it has the problem of having to include it
in each cell. This seems to me better because it keeps the consistency of the
column declarations. Plus, the style file required to implement this is
much smaller than that for DECALIGN.
 
An unexpected benefit of using the \dec approach is that other entries in the
column need not be decimal aligned and are easily manipulated. For example, at
the bottom of a column of regression coefficients it is customary to have the
number of cases, the r-square and assorted other stuff. These entries are
probably best given right aligned, which is easily done when using \dec.
 
I've put together a little file called DECTAB.STY which is appended below. It
steals the \dec definitions from REVTEX and adds a little for convenience.
You may want to redefine \dec to \da or even \d to reduce the required typing
in tables. I've stuck with \dec simply for clarity. DECTAB.STY also provides
\la, \ra and \ca for local left, right and center alignment. This is often
convenient and again saves typing.
 
I've tried it for one whole day on my tables and it seems to work. Beyond
that, I offer no warranties. If you find problems with it, please let me know.
 
Once more, thanks to all who sent their advice. Even if I don't take it, I
have profited from it.
----------------------------Begin DECTAB.STY--------------------------------
% DECTAB.STY  (April 27, 1991)
% Allows decimal alignment in tabular environment
% \dec definitions taken from REVTEX.STY
% by Charles Franklin, April 27, 1991
% (C38871CF@WUVMD.WUSTL.EDU or C38871CF@WUVMD.Bitnet)
%
% USAGE:  For decimal alignment in a table, use \dec 3.14 for
%         the cell entry.  The column should be center aligned
%         to achieve the desired effect.
%         For example:
%
%         \begin{tabular}{lcc}
%
%         Constant          & \dec  -1.461    &  \dec  -0.724  \\
%         Standard Error    & \dec  (0.422)   &  \dec  (0.455) \\
%
%         Note that a `.' MUST appear for the alignment to work.
%         Use `\dec 520.' NOT `\dec 520' for integers.
%
%         DECTAB also defines \ra, \la, \ca for easy modification of
%         global alignments. These produce local right, left and center
%         alignments of the cell entry. If there are spaces in the cell
%         entry, enclose the contents in {...}, eg \la {This Column}
%
\typeout{Document Style Option `dectab', version April 27, 1991}
 
\newdimen\@Ldec \newdimen\@Rdec
 
\def\dec #1.#2 {\hbox to\@Ldec{\hss#1}\def\test{#2}%
\ifx\test\empty\hbox to\@Rdec{\hfill}\else\hbox to\@Rdec{.#2\hss}\fi
}
 
\def\setdec #1.#2 {\relax%
  \bgroup
    \setbox0\hbox{\kern1pt\relax#1}\setbox1\hbox{\kern1pt\relax#2}%
    \global\@Ldec\wd0\global\@Rdec\wd1%
  \egroup
}
 
\setdec 000.000 % default size of 3 digits on each side
 
% Following defs allow easy modification of global alignment in
% tables. \ra, \la, \ca for right, left and center alignments.
 
\def\ra #1 {\multicolumn{1}{r}{#1}}
\def\la #1 {\multicolumn{1}{l}{#1}}
\def\ca #1 {\multicolumn{1}{c}{#1}}
 
% end DECTAB.STY