Extract the numerical and non-numerical portion from text

Question

I would like to extract the leading number and subsequent text from a string. I have an idea of using the xstring package to gobble characters from the right until I end up with a number or an empty string, but wondering if there is an easier way to do it. The leading number is all the text up until the first character that is not a digit, period, or a plus and minus sign.

Don't really need to worry about error cases such as:

• an additional +, - within the number
• more digits after first non-numerical digit

So, I should get the following output with the definitions of \ExtractLeadingNumber and \ExtractTralingNonDigits completed:

Code:

\documentclass[border=2pt]{standalone}
\usepackage{booktabs}
\newcommand{\ExtractLeadingNumber}[1]{#1}%
\newcommand{\ExtractTralingNonDigits}[1]{#1}%
% ignore #2 and #3 as those are only needed to produce the desired output
\newcommand{\Test}[3]{#1&\ExtractLeadingNumber{#1}&\ExtractTralingNonDigits{#1}\}%
%\newcommand{\Test}[3]{#1&#2&#3\}% This produces desired output
\begin{document}
\begin{tabular}{l r r r}
 & &Number &Non-Digits\
\midrule
Decimal:
&\Test{ 1.01abc}{ 1.01}{abc}
&\Test{+2.01abc}{+2.01}{abc}
&\Test{-3.01abc}{-3.01}{abc}
\midrule
Integer:
&\Test{  abc}{  }{abc}
&\Test{ 5abc}{ 5}{abc}
&\Test{+6abc}{+6}{abc}
&\Test{-7abc}{-7}{abc}
\midrule
Floating Point:
&\Test{ 5.34abc}{ 5.34}{abc}
&\Test{+6.34abc}{+6.34}{abc}
&\Test{-7.34abc}{-7.34}{abc}
\midrule
Number Only:
&\Test{3}{3}{}
&\Test{3.2}{3.2}{}
&\Test{-5.1}{-5.1}{}
&\Test{+5.1}{+5.1}{}
\midrule
No Digits:
&\Test{abc}{}{abc}
\midrule
Formatted Text:
&\Test{  8$abc_1$}{  8}{$abc_1$}
&\Test{-8.2$abc_1$}{-8.2}{$abc_1$}
&\Test{+$abc_1$}{+}{$abc_1$}
&\Test{$abc_1$}{}{$abc_1$}% no digits
\end{tabular}
\end{document}

Answer 1

An approach using the LaTeX3 l3regex module

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{array,booktabs,expl3,l3regex}
\ExplSyntaxOn
\tl_new:N \l_extract_tl
\regex_set:Nn \l_extract_tl { ^\s*([+-]?\d*\.?\d*)\s*(.*) }
\seq_new:N \l_extract_seq
\tl_new:N \NumberValue
\tl_new:N \OtherValue
\cs_new_protected:Npn \extract_number:n #1
  {
    \regex_extract_once:NnN  \l_extract_tl {#1} \l_extract_seq
    \tl_gset:Nx \NumberValue { \seq_item:Nn \l_extract_seq { 2 } }
    \tl_gset:Nx \OtherValue { \seq_item:Nn \l_extract_seq { 3 } }
  }
\cs_new_protected:Npn \Test #1
  {
    \extract_number:n {#1}
    & \detokenize{#1} & \NumberValue & \OtherValue
  }
\ExplSyntaxOff
\begin{document}
\begin{tabular}{l>{\ttfamily}r>{\ttfamily}r>{\ttfamily}r}
  \toprule
             & \multicolumn{1}{r}{Input} & 
               \multicolumn{1}{r}{Digit} & \multicolumn{1}{r}{Non-digit} \\
  \midrule
   Decimal:  \Test{ 1.01abc}               \\
             \Test{+2.01abc}               \\ 
             \Test{-3.01abc}               \\
  \midrule
   Integer:  \Test{  abc}                  \\
             \Test{ 5abc}                  \\ 
             \Test{+6abc}                  \\
             \Test{-7abc}                  \\
  \midrule
   Floating Point: \Test{ 5.34abc}         \\
                   \Test{+6.34abc}         \\
                   \Test{-7.34abc}         \\
  \midrule
   Number Only:    \Test{3}                \\
                   \Test{3.2}              \\ 
                   \Test{-5.1}             \\
                   \Test{+5.1}             \\
  \midrule
   No Digits:      \Test{abc}              \\
  \midrule
   Formatted Text: \Test{  8$abc_1$}       \\ 
                   \Test{-8.2$abc_1$}      \\ 
                   \Test{+$abc_1$}         \\
                   \Test{$abc_1$}          \\
  \bottomrule
\end{tabular}
\end{document}

Currently, this module is 'experimental' hence loading it separately from expl3, but I'd expect it to move to 'kernel' in the near-ish future (before the end of the year).

The way that this works is that when we do a regular expression match, the capturing groups are stored in a sequence indexed from 0 (the complete match) upward. So I've got the first capture group as the numerical part and the second as the non-numerical. Notice that I've also included \s* to remove any leading spaces from those two groups: if you miss that out then you'll also pick up the spaces as part of the match.

Also notice that the results here are detokenized, so if you want to have formatted text you'd need to \scantokens the results. (Something as simple as \scantokens\expandafter{\OtherValue} would do here.)

Answer 2

If you can use luatex, you may use a proper parser (the code below is in ConTeXt, just because I don't know all the details of using luatex in LaTeX).

 \startluacode
  local P, R, S, V, match = lpeg.P, lpeg.R, lpeg.S, lpeg.V, lpeg.match
  local Ct, C, Cs, Cc = lpeg.Ct, lpeg.C, lpeg.Cs, lpeg.Cc

  local format = string.format

  local digit    = R("09")
  local sign     = S('+-')
  local integer  = sign^0 * digit^0 -- NOTE: I'd rather use digit^1, but
                                    -- the requirements want to capture a
                                    --  single sign as well
  local float    = sign^0 * digit^0 * P('.') * digit^1
  local space    = P(" ")^0

  local number   = Cs(float + integer)
  local any      = Cs(P(1)^0)

  local number_value = Cc("\\global\\def\\NumberValue{%s}") * number / format
  local other_value  = Cc("\\global\\def\\OtherValue{%s}")  * any    / format
  local parser = Cs(space * number_value * other_value)

  function commands.extract_number(s)
      context(match(parser,s))
  end
\stopluacode

\unprotect
\def\extract#1%
    {\let\NumberValue\relax
     \let\OtherValue \relax
     \ctxcommand{extract_number(\!!bs\detokenize{#1}\!!es)}}
\protect

You can then use this as follows.

\def\Test#1%
    {\extract{#1}%
     #1 \NC \NumberValue \NC \OtherValue}

\starttext

\starttabulate[|l|r|r|r|]
  \HL
  \NC           \NC Input \NC Digit \NC Non-Digit \NC \NR
  \HL
  \NC Decimal:  \NC \Test{ 1.01abc}               \NC \NR
  \NC           \NC \Test{+2.01abc}               \NC \NR 
  \NC           \NC \Test{-3.01abc}               \NC \NR
  \HL
  \NC Integer:  \NC \Test{  abc}                  \NC \NR
  \NC           \NC \Test{ 5abc}                  \NC \NR 
  \NC           \NC \Test{+6abc}                  \NC \NR
  \NC           \NC \Test{-7abc}                  \NC \NR
  \HL
  \NC Floating Point: \NC \Test{ 5.34abc}         \NC \NR
  \NC                 \NC \Test{+6.34abc}         \NC \NR
  \NC                 \NC \Test{-7.34abc}         \NC \NR
  \HL
  \NC Number Only:    \NC \Test{3}                \NC \NR
  \NC                 \NC \Test{3.2}              \NC \NR 
  \NC                 \NC \Test{-5.1}             \NC \NR
  \NC                 \NC \Test{+5.1}             \NC \NR
  \HL
  \NC No Digits:      \NC \Test{abc}              \NC \NR
  \HL
  \NC Formatted Text: \NC \Test{  8$abc_1$}       \NC \NR 
  \NC                 \NC \Test{-8.2$abc_1$}      \NC \NR 
  \NC                 \NC \Test{+$abc_1$}         \NC \NR
  \NC                 \NC \Test{$abc_1$}          \NC \NR
  \HL
\stoptabulate
\stoptext

which gives

Answer 3

Here is a solution with xstring:

\documentclass[border=2pt]{standalone}
\usepackage{booktabs}
\usepackage{xstring}
\makeatletter
% first, need to fix a bug in xstring:
\@xs@newmacro\IfDecimal{}{1}{0}{%
    \@xs@formatnumber{#1}\@xs@reserved@A
    \decimalpart\z@
    \afterassignment\@xs@defafterinteger\integerpart\@xs@reserved@A\relax\@xs@nil
    \expandafter\@xs@testdot\@xs@afterinteger\@xs@nil
    \ifx\@empty\@xs@afterdecimal\expandafter\@firstoftwo\else\expandafter\@secondoftwo\fi}

\newcommand*\Test[1]{%
    \IfBeginWith{#1}{ }{\StrBehind{#1}{ }[\temp@@]}{\def\temp@@{#1}}%
    \IfDecimal\temp@@
        {\def\temp@{#1&#1&}}
        {\def\temp@{#1&}%
        \StrBefore{#1}\@xs@afterdecimal[\temp@@]%
        \expandafter\g@addto@macro\expandafter\temp@\expandafter{\temp@@&}%
        \expandafter\g@addto@macro\expandafter\temp@\expandafter{\@xs@afterdecimal}%
        }%
    \temp@\\}
\makeatother
\begin{document}
\begin{tabular}{l r r r}
 & &Number &Non-Digits\\
\midrule
Decimal:
&\Test{ 1.01abc}
&\Test{+2.01abc}
&\Test{-3.01abc}

\midrule
Integer:
&\Test{  abc}
&\Test{ 5abc}
&\Test{+6abc}
&\Test{-7abc}

\midrule
Floating Point:
&\Test{ 5.34abc}
&\Test{+6.34abc}
&\Test{-7.34abc}

\midrule
Number Only:
&\Test{3}
&\Test{3.2}
&\Test{-5.1}
&\Test{+5.1}

\midrule
No Digits:
&\Test{abc}

\midrule
Formatted Text:
&\Test{  8$abc_1$}
&\Test{-8.2$abc_1$}
&\Test{+$abc_1$}
&\Test{$abc_1$}
\end{tabular}
\end{document}

EDIT: here is how to do with \ExtractLeadingNumber and \ExtractTralingNonDigits

\makeatletter
% first, need to fix a bug in xstring:
\@xs@newmacro\IfDecimal{}{1}{0}{%
    \@xs@formatnumber{#1}\@xs@reserved@A
    \decimalpart\z@
    \afterassignment\@xs@defafterinteger\integerpart\@xs@reserved@A\relax\@xs@nil
    \expandafter\@xs@testdot\@xs@afterinteger\@xs@nil
    \ifx\@empty\@xs@afterdecimal\expandafter\@firstoftwo\else\expandafter\@secondoftwo\fi}

\newcommand*\ExtractLeadingNumber[1]{%
    \IfBeginWith{#1}{ }{\StrBehind{#1}{ }[\temp@@]}{\def\temp@@{#1}}%
    \IfDecimal\temp@@{#1}{\StrBefore{#1}\@xs@afterdecimal}%
}
\newcommand*\ExtractTralingNonDigits[1]{%
    \IfBeginWith{#1}{ }{\StrBehind{#1}{ }[\temp@@]}{\def\temp@@{#1}}%
    \IfDecimal\temp@@{}\@xs@afterdecimal
}
\makeatother

\newcommand*\Test[1]{#1&\ExtractLeadingNumber{#1}&\ExtractTralingNonDigits{#1}\\}

Answer 4

I can show the plain TeX solution of this problem for the sake of completeness.

\def\separeparts#1{\def\firstpart{}\def\listchars{0123456789.}\separepartsA#1\end}
\def\separepartsA#1{\isinlist{+-}#1%
   \iftrue
      \def\firstpart{#1}\expandafter\separepartsB
   \else 
      \def\next{\separepartsB#1}\expandafter\next
   \fi
}
\def\separepartsB#1{\isinlist\listchars#1%
   \iftrue
      \addto\firstpart#1%
      \ifx.#1\def\listchars{0123456789}\fi
      \expandafter\separepartsB
   \else
      \def\next{\separepartsC#1}\expandafter\next
   \fi
}
\def\separepartsC#1\end{\def\secondpart{#1}}

Note that the list of allowed digits \listchars includes decimal point but if decimal point is found then \listchars is redefined because the second decimal point isn't allowed.

This code needn't any package, only two macros from opmac.tex is used. You can copy and paste these macros from opmac.tex or from here:

\def\isinlist#1#2#3{\def\tmp##1#2##2\end{\def\tmp{##2}%
   \ifx\tmp\empty \csname iffalse\expandafter\endcsname \else
                  \csname iftrue\expandafter\endcsname \fi}% end of \def\tmp
   \expandafter\tmp#1\endlistsep#2\end
}
\long\def\addto#1#2{\expandafter\def\expandafter#1\expandafter{#1#2}}

Now, you can do tests:

\def\test#1{\separeparts{#1}
   \immediate\write16{"#1" = "\firstpart" and "\secondpart"}
}

\test{+2.01abc}   % output: "+2.01abc" = "+2.01" and "abc"
\test{-3.01abc}   % output: "-3.01abc" = "-3.01" and "abc"

\test{  abc}      % output: " abc" = "" and "abc"
\test{ 5abc}      % output: " 5abc" = "5" and "abc"
\test{+6abc}      % output: "+6abc" = "+6" and "abc"

\test{1.23.36abc} % output: "1.23.36abc" = "1.23" and ".36abc"

You can use this code in plain TeX, in LaTeX or in ConTeXt. It doesn't matter. The code is based only on TeX primitives.