Testing for number

Question

How do I test if a given parameter is a number, in order to apply a different style? And if not, just ignore... Like:

\domorestuffifnumber{things} -> things
\domorestuffifnumber{123}    -> \emph{123}

Thanks.

Answer 1

\documentclass{article}

\def\isnum#1{%
  \if!\ifnum9<1#1!\fi%
     \emph{#1}%
  \else#1%
  \fi}

\begin{document}

\isnum{dummy}
\isnum{123}

\end{document}

If #1 is a number, we have \ifnum9<1xxx, which is true and therefore empty, which leads to \if!!, which is also true, and \emph{#1} is the output. In the other case we have (#1 mybe 0a) \ifnum9<10a, which is true and leaves a. Therefore we compare \if!a, which is wrong, the reason why now the \else part is the output.

Caveat: Does not work for numbers > 999999999.

Answer 2

Here's a slightly flawed, but slightly more generic thing than you're asking for.

\documentclass{article}
\usepackage{etoolbox}
\makeatletter
\newcommand\ifnumber[1]{%
        \begingroup
        \edef\temp{#1}%
        \expandafter\ifstrempty\expandafter{\temp}
                {\endgroup\@secondoftwo}
                {\expandafter\ifnumber@i\temp\@nnil}%
}
\def\ifnumber@i#1#2\@nnil{%
        \if-#1%
                \ifstrempty{#2}
                        {\def\temp{X}}
                        {\def\temp{#2}}%
        \else
                \def\temp{#1#2}%
        \fi
        \afterassignment\ifnumhelper
        \count@0\temp\relax\@nnil
        \endgroup
}

\def\numrelax{\relax}%
\def\ifnumhelper#1\@nnil{%
        \def\temp{#1}%
        \ifx\temp\numrelax
                \aftergroup\@firstoftwo
        \else
                \aftergroup\@secondoftwo
        \fi
}
\makeatother

\newcommand\testnumber[1]{#1: \ifnumber{#1}{Number}{Not a number}\par}
\begin{document}
\def\foo{-55}
\testnumber{1234}
\testnumber{\foo}
\testnumber{-}
\testnumber{}
\testnumber{1}
\testnumber{1234abc}
\testnumber{abc1234}
\end{document}

It's slightly complicated by checking if the first token in the expansion of the argument is a -. Unfortunately, it does not work if the argument is a register. (It probably doesn't work in other cases too.)

But from the \ifnumber macro, you should easily be about to build what you want.

\newcommand\domorestuffifnumber[1]{\ifnumber{#1}{\emph{#1}}{#1}}

Answer 3

This is a somewhat late answer, but I am including it here for completeness. When TeX is expecting a number a trailing zero will be ignored if it is followed by another number. However, if the 0 is followed by a non-number it will stop the scanning and insert the letter in the stream. The macro that follows capitalizes on this fact. We set a counter this way within a box. If it is a number the input gets fully absorbed and the width of the box is zero. If it is not a number the box will contain the non-numbers and hence its width will be greater than zero. By testing for the width of the box we can know if the input was a number or not.

\documentclass{article}
\makeatletter
\def\add@zero#1{0#1}
\def\isNum#1{%
   \sbox\z@{\@tempcnta=0#1\relax}
   %\setbox0\hbox{\expandafter\@tempcnta\expandafter\add@zero\numtest\relax}
   \ifdim\wd0>\z@\relax\@latex@warning{Not a number!}\else is numeric\fi
}

\begin{document}
\isNum{13}

% Handles registers
\isNum{\the\@tempcnta}

%warning for not a number
\isNum{dummy}
\makeatother
\end{document}

Empty input is treated a zero, and this can be useful in many situations.

(Edit: simplified as per egreg's comments)

Answer 4

A LuaTeX solution:

\documentclass{article}
\begin{document}

\directlua{ dofile("myluastuff.lua") }

\newcommand\domorestuffifnumber[1]{%
  \directlua{ 
    domorestuffifnumber("#1") 
}}

\def\foo{-55}
\domorestuffifnumber{1234}
\domorestuffifnumber{\foo}
\domorestuffifnumber{-}
\domorestuffifnumber{}
\domorestuffifnumber{1}
\domorestuffifnumber{1234abc}
\domorestuffifnumber{abc1234}
\end{document}

and the myluastuff.lua file:

function domorestuffifnumber( arg )
  if tonumber(arg) then 
    tex.sprint("\\emph{" .. arg .. "}") 
  else
    tex.sprint(arg or "")
 end
end

I think the solution is quite readable.

Answer 5

The xstring package provides two commands: \IfInteger and \IfDecimal. Each of them uses the syntax

\IfInteger{<value being tested>}{<result if true>}{<result if false>}

If you don't want to differentiate between integers and decimals, we could do

\documentclass{article}
\usepackage{xstring}

\newcommand{\DoStuff}[1]{\emph{#1}}

\newcommand{\IfNumber}[1]
{%
  \IfInteger{#1}
    {\DoStuff{#1}}
    {%
      \IfDecimal{#1}
        {\DoStuff{#1}}
        {#1}%
    }%
}

\begin{document}

\IfNumber{123}

\IfNumber{123.123}

\IfNumber{abc}

\end{document}

Answer 6

I'd like to present another solution that is able to parse integer and floating point numbers. Usage of the main macro is

\ifnumber[<optional setup>]{<tokens>}{<true part>}{<false part>}

where <tokens> is the string to be tested whether it represents a number. <optional setup> is an optional list of definitions to modify the way numbers are parsed (see below). By default numbers are parsed as floating point numbers with optional signs.

Pros

• Pure LaTeX implementation, no extra libraries required.
• Provides some basic customization. Currently supported are
  • enabling/disabling of parsing optional signs (\let\parsesign=\iftrue/\iffalse),
  • enabling/disabling of parsing the floating point part (\let\parsefloat=\iftrue/\iffalse), and
  • definition of tokens that represent +, - and . (\parse@num@minus, \parse@num@plus and \parse@num@point, respectively).
• The main parsing macro \parse@num is fully expandable, given that the setup macros are in scope.
• The parsing macros correspond to states in a DFA, so more extensions should be quite easy to implement.

Cons

• Register values cannot be passed directly to \ifnumber but have to be expanded via \the or \number before.
• Macros in the string are not expanded properly.

Full example:

\documentclass{article}

\makeatletter

% Some conditional tests
\def\@genericif#1{#1\expandafter\@firstoftwo\else\expandafter\@secondoftwo\fi}
\def\@ifdigit#1{\@genericif{\ifnum1<1\noexpand#1\relax}}
\def\@ifempty#1{\@genericif{\if\relax\detokenize{#1}\relax}}

% The main parsing macros
\def\parse@num#1{%
    \@ifempty{#1}%
        {\parse@num@false}%
        {\@genericif{\parsesign}%
            {\parse@num@sign#1{}\@end}%
            {\parse@num@dig#1{}\@end}%
        }%
}
% Parse sign
\def\parse@num@sign#1#2\@end{%
    \@genericif{\ifx\parse@num@minus#1}%
        {\@ifempty{#2}{\parse@num@false}{\parse@num@dig#2\@end}}%
        {\@genericif{\ifx\parse@num@plus#1}%
            {\@ifempty{#2}{\parse@num@false}{\parse@num@dig#2\@end}}%
            {\parse@num@dig#1#2\@end}%
        }%
}
% Parse first digit
\def\parse@num@dig#1#2\@end{%
    \@ifdigit{#1}%
        {\@ifempty{#2}{\parse@num@true}{\parse@num@digs#2\@end}}%
        {\parse@num@false}%
}
% Parse optional following digits
\def\parse@num@digs#1#2\@end{%
    \@ifdigit{#1}{%
        \@ifempty{#2}%
            {\parse@num@true}%
            {\parse@num@digs#2\@end}%
    }{%
        \@genericif{\parsefloat}{%
            \@genericif{\ifx\parse@num@point#1}%
                {\@ifempty{#2}{\parse@num@false}{\parse@num@decs#2\@end}}%
                {\parse@num@false}%
        }{\parse@num@false}%
    }%
}
% Parse decimal places
\def\parse@num@decs#1#2\@end{%
    \@ifdigit{#1}{%
        \@ifempty{#2}%
            {\parse@num@true}%
            {\parse@num@decs#2\@end}%
    }{\parse@num@false}%
}

% User interface
\newcommand\ifnumber[4][]{%
    \begingroup
    \let\parsesign=\iftrue
    \let\parsefloat=\iftrue
    \let\parse@num@minus=-%
    \let\parse@num@plus=+%
    \let\parse@num@point=.%
    #1%
    \def\parse@num@true{\endgroup#3}%
    \def\parse@num@false{\endgroup#4}%
    \parse@num{#2}%
}

\makeatother

\begin{document}
\newcommand\testnum[2][]{%
    \makebox[5em][l]{#2}%
    \makebox[5em][l]{\ifnumber[#1]{#2}{yes}{no}}%
}
\ttfamily
default setting\par
\testnum{}
\testnum{0}\par
\testnum{1}
\testnum{12345}\par
\testnum{+}
\testnum{+123}\par
\testnum{-}
\testnum{-123}\par
\testnum{-0}
\testnum{+0}\par
\testnum{0.}
\testnum{0.123}\par
\testnum{-.1}
\testnum{-+123}\par
\testnum{-0.123}
\testnum{+0.123}\par
\testnum{abc}
\testnum{123abc}\par

\medskip
\string\parsesign\ = \string\iffalse\par
\testnum[\let\parsesign=\iffalse]{123.45}\par
\testnum[\let\parsesign=\iffalse]{+123.45}\par
\testnum[\let\parsesign=\iffalse]{-123.45}\par

\medskip
\string\parsefloat\ = \string\iffalse\par
\testnum[\let\parsefloat=\iffalse]{123}
\testnum[\let\parsefloat=\iffalse]{123.45}\par
\testnum[\let\parsefloat=\iffalse]{+123}
\testnum[\let\parsefloat=\iffalse]{+123.45}\par
\testnum[\let\parsefloat=\iffalse]{-123}
\testnum[\let\parsefloat=\iffalse]{-123.45}\par

\medskip
\makeatletter
\string\parse@num@point\ = ,\par
\testnum[\let\parse@num@point=,]{-123,45}
\testnum[\let\parse@num@point=,]{0.12}\par
\makeatother
\end{document}