Is it possible to re-group every 4 digits in a number with siunitx package?

Question

The current default digit grouping option in the package siunitx gives me a large number comma-separated or space-separated every 3 digits, e.g.

\documentclass{article}

\usepackage[utf8]{inputenc}
\usepackage{siunitx}

\begin{document}

   \num[group-separator={,}]{123456789}

\end{document}

would give me 123,456,789. Is it possible to change it so that I get 1,2345,6789?

I can't find an answer in the siunitx documentation or elsewhere on the Internet. I am also happy to know if there is an alternative package that handles number formatting and typesetting automatically just like siunitx, but allows this re-grouping. Thanks in advance!

Welcome to TeX.SX! I don't think it's possible with the current version of siunitx. — egreg, Feb 11 '18 at 14:03
Can you point to a place where such grouping is used? I can only think of something like credit card numbers, which is well out-of-scope. — Joseph Wright, Feb 11 '18 at 14:05
@egreg Thanks, but I am also happy to know if there is another number formatting package that would allow me to do this. — MikeW, Feb 11 '18 at 14:06
If I remember correctly there is some other package that allows to group differently - search for grouping phone number in tex. — samcarter_is_at_topanswers.xyz, Feb 11 '18 at 14:06
Yes, in Chinese and Japanese languages, large numbers are usually multiples of 10,000 rather than 10^3. — MikeW, Feb 11 '18 at 14:06
@MikeW Do you mean in technical published work? I'm happy to look at such features but I'd want links to professionally-typeset work. — Joseph Wright, Feb 11 '18 at 14:09
@JosephWright I am afraid I don't have any links as it's just for my own LaTeX notes and presentations. I do admit I am somewhat pedantic... — MikeW, Feb 11 '18 at 14:12
@samcarter Thanks for the tips, I will have a look at phone number grouping packages. — MikeW, Feb 11 '18 at 14:13
related question: https://tex.stackexchange.com/a/145000/36296 — samcarter_is_at_topanswers.xyz, Feb 11 '18 at 14:26
@samcarter Thanks for the link, didn't know the Indian system was different as well. Seems the problem is more advanced than I thought! — MikeW, Feb 11 '18 at 14:34

egreg · Accepted Answer · 2018-02-11T20:27:02.310

There's currently no support for this in siunitx. You can do it with some different code:

\documentclass{article}
\usepackage{xparse,siunitx}

\ExplSyntaxOn

\NewDocumentCommand{\groupfour}{O{,}m}
 {
  \mikew_groupfour:nn { #1 } { #2 }
 }

\tl_new:N \l_mikew_groupfour_separator_tl
\tl_new:N \l_mikew_groupfour_number_tl

\cs_new_protected:Nn \mikew_groupfour:nn
 {
  \tl_set:Nn \l_mikew_groupfour_separator_tl { {#1} }
  \tl_set:Nx \l_mikew_groupfour_number_tl { #2 }
  \tl_replace_all:Nnn \l_mikew_groupfour_number_tl { ~ } { }
  \tl_reverse:N \l_mikew_groupfour_number_tl
  \regex_replace_all:nnN
   { [0-9]{4} } % search
   { \0 \c{l_mikew_groupfour_separator_tl} } % replace
   \l_mikew_groupfour_number_tl % token list
  \tl_reverse:N \l_mikew_groupfour_number_tl
  \regex_replace_once:nnN
   { \A \c{l_mikew_groupfour_separator_tl} }
   { }
   \l_mikew_groupfour_number_tl
  \tl_use:N  \l_mikew_groupfour_number_tl
 }

\ExplSyntaxOff

\begin{document}

\groupfour{ 123456789 }

\groupfour[\,]{1 2345 6789}

$\groupfour{12345678}$ % test for math mode

\end{document}

This reverses the input, after removing blank spaces; then after every group of four digits, the separator is inserted (in symbolic form); the string is reversed again and a leading separator is removed.

You can change the separator by calling \groupfour[<separator>]{<number>}.

An extended version for dealing also with decimal numbers. In the decimal part, groups of four digits are separated by thin spaces. It wouldn't be difficult to change it, according to needs.

\documentclass{article}
\usepackage{xparse,siunitx}

\ExplSyntaxOn

\NewDocumentCommand{\groupfour}{O{,}m}
 {
  \mikew_groupfour:nn { #1 } { #2 }
 }

\tl_new:N \l_mikew_groupfour_separator_tl
\tl_new:N \l_mikew_groupfour_number_tl
\seq_new:N \l_mikew_groupfour_parts_seq

\cs_new_protected:Nn \mikew_groupfour:nn
 {
  \tl_set:Nn \l_mikew_groupfour_separator_tl { {#1} }
  \regex_split:nnN { \. } { #2 } \l_mikew_groupfour_parts_seq
  \tl_set:Nx 
   \l_mikew_groupfour_number_tl
   { \seq_item:Nn \l_mikew_groupfour_parts_seq { 1 } }
  \tl_replace_all:Nnn \l_mikew_groupfour_number_tl { ~ } { }
  \tl_reverse:N \l_mikew_groupfour_number_tl
  \__mikew_groupfour_replace:
  \tl_reverse:N \l_mikew_groupfour_number_tl
  \tl_use:N  \l_mikew_groupfour_number_tl
  \int_compare:nT { \seq_count:N \l_mikew_groupfour_parts_seq > 1 }
   {
    \tl_set:Nn \l_mikew_groupfour_separator_tl { {\,} }
    . % print the decimal point
    \tl_set:Nx 
     \l_mikew_groupfour_number_tl
     { \seq_item:Nn \l_mikew_groupfour_parts_seq { 2 } }
    \__mikew_groupfour_replace:
    \tl_use:N  \l_mikew_groupfour_number_tl
   }
 }

\cs_new_protected:Nn \__mikew_groupfour_replace:
 {
  \regex_replace_all:nnN
   { [0-9]{4} } % search
   { \0 \c{l_mikew_groupfour_separator_tl} } % replace
   \l_mikew_groupfour_number_tl % token list
  \regex_replace_once:nnN
   { \c{l_mikew_groupfour_separator_tl} \Z }
   { }
   \l_mikew_groupfour_number_tl
 }

\ExplSyntaxOff

\begin{document}

X\groupfour{ 123456789 }X

X\groupfour[\,]{1 2345 6789}X

X$\groupfour{12345678}$X

X\groupfour{1234567890.12345678}X

\end{document}

Thanks for the interesting answer. I have just tried it and it works! — MikeW, Feb 11 '18 at 14:31

Mico · Answer 2 · 2018-02-14T17:55:49.540

For the sake of variety, here's a LuaLaTeX-based solution. It's very similar to to the one given in this answer. The solution defines a user macro called \groupfour, which invokes a Lua function that does the actual work. If the number (the argument of \groupfour) contains a decimal part, no commas are inserted in the decimal portion.

% !TEX TS-program = lualatex
\documentclass{article}
\usepackage{siunitx}
\usepackage{luacode}
\begin{luacode}

function groupfour ( s )
    z = ""
    -- Check if number contains a decimal part. If so, don't
    -- insert commas in the decimal part.
    n = string.find ( s, "%." ) 
    if n then
       -- Set aside decimal part of number in string "z"
       z = string.sub ( s , n )
       s = string.sub ( s , 1 , n-1 )
    end 
    t = ""
    while string.len ( s ) > 4 do
        t = "{,}" .. string.sub ( s, -4 ) .. t
        s = string.sub ( s , 1, -5 ) 
    end
    tex.sprint ( s .. t .. z )
end

\end{luacode}
\newcommand\groupfour[1]{\directlua{groupfour(\luastring{#1})}}

\begin{document}
\num[group-separator={,}]{123456789}

\groupfour{123456789}
\end{document}

Is it possible to re-group every 4 digits in a number with siunitx package?

2 Answers2