Making letters of a word appear in random order

Question

The context is a kids game where a sequence of questions appear on screen, one at a time, and the answers appear gradually and randomly one letter at a time by the press of some button.

For example, ``Question 1 : What is the capital of Italy ?'' The answer appears as a blank of unspecified number of characters, and by press of some button perhaps E shows up and then - - R - - E - -, and then one by one all the way to - -ROME- -. Or a similar arrangement.

What is the instrument for this? How do I make the letters show up randomly.

As a slide show, each slide shows a slightly different image. OTOH, the letters always show up in the same order (pseudo-random or not). You might need to put each letter into a \makebox or tikz node to keep the spacing constant. — John Kormylo, Apr 30 '20 at 14:01
I'd use OCGs and a bit of JavaScript for the random bit. But kerning and ligatures will get lost, because characters have to be treated one by one. Perhaps I would choose caps or small caps for the answers. — AlexG, Apr 30 '20 at 18:09

score 1 · Accepted Answer · 2020-05-01T06:08:03.890

Here is something that does that. I am also writing this because apart from the memberQ macro, which is more or less taken from here, it defines pgf functions randompermutation(<n>), which yields a random permutation of integers {1,...,<n>}, and take, which returns a sublist. The macro defined based on these functions and the parser module is \ShowPartially. In order to use it on a word, you have to first "initialize" it, e.g.

 \ShowPartially{initial,n=2,word=Murmeltier}

Then one permutation of the numbers {1,...,<# of characters>} is stored and you can show e.g. 4 random letters with

 \ShowPartially{n=4}

That way the results for larger n will always the letters that show for smaller n. If you want to create a new permutation list, just call \ShowPartially again with the initial key.

\documentclass{article}
\usepackage{pgf}
\usepgfmodule{parser}
\makeatletter
%membership test    
\pgfmathdeclarefunction{memberQ}{2}{%
  \begingroup%
    \edef\pgfutil@tmpb{0}%memberQ({\lstPast},\inow)
    \edef\pgfutil@tmpa{#2}%
    \expandafter\pgfmath@member@i#1\pgfmath@token@stop
    \edef\pgfmathresult{\pgfutil@tmpb}%
    \pgfmath@smuggleone\pgfmathresult%
  \endgroup}
\def\pgfmath@member@i#1{%
    \ifx\pgfmath@token@stop#1%
    \else
      \edef\pgfutil@tmpc{#1}%
      \ifx\pgfutil@tmpc\pgfutil@tmpa\relax%
      \gdef\pgfutil@tmpb{1}%
      \fi%
      \expandafter\pgfmath@member@i
    \fi}  
\pgfmathdeclarefunction{randompermutation}{1}{%
\begingroup%          
\c@pgf@counta=0%
\edef\pgfutil@tmpa{0}%
\loop
\advance\c@pgf@counta by1%
\edef\pgfutil@tmpa{\pgfutil@tmpa,\the\c@pgf@counta}%
\ifnum\c@pgf@counta<#1\relax
\repeat
\loop
\advance\c@pgf@counta by-1%
\pgfmathtruncatemacro{\pgfutil@tmpb}{1+rnd*\c@pgf@counta}%
\pgfmathtruncatemacro{\pgfutil@tmpc}{{\pgfutil@tmpa}[\pgfutil@tmpb]}%
\ifnum\c@pgf@counta=\numexpr#1-1\relax
\edef\pgfmathresult{\pgfutil@tmpc}%
\else
\edef\pgfmathresult{\pgfmathresult,\pgfutil@tmpc}%
\fi
\edef\pgfutil@tmpd{\pgfutil@tmpa}%
\edef\pgfutil@tmpa{0}%
\pgfutil@for\my@item:={\pgfutil@tmpd}\do{%
\unless\ifnum\pgfutil@tmpc=\my@item
\unless\ifnum\my@item=0\relax
\edef\pgfutil@tmpa{\pgfutil@tmpa,\my@item}%
\fi\fi}%
\ifnum\c@pgf@counta>0\relax
\repeat
\pgfmath@smuggleone\pgfmathresult%
\endgroup}
\pgfmathdeclarefunction{take}{2}{%
\begingroup%
\c@pgf@counta=0%
\pgfutil@for\my@item:={#1}\do{%
\advance\c@pgf@counta by1%
\ifnum\c@pgf@counta<#2\relax
\ifnum\c@pgf@counta=1\relax
\edef\pgfmathresult{\my@item}%
\else
\edef\pgfmathresult{\pgfmathresult,\my@item}%
\fi\fi}%
\pgfmath@smuggleone\pgfmathresult%
\endgroup}
\makeatother    
\newif\ifhideletterinitial
\hideletterinitialfalse
\pgfkeys{/hide letter/.cd,initial/.is if=hideletterinitial,n/.initial=1,
word/.initial=Rome}
\newcounter{letterpos}
\pgfparserdef{letterhide}{all};{\pgfparserswitch{final}}% 
\pgfparserdefunknown{letterhide}{all}%
{\stepcounter{letterpos}%
\unless\ifhideletterinitial
\pgfmathtruncatemacro{\itest}{memberQ({\mysublist},\number\value{letterpos})}%
\ifnum\itest=1\relax
\pgfparserletter
\else
\phantom{\pgfparserletter}%
\fi
\fi}% \pgfparserletter
\pgfparserset{letterhide/silent=true}%
\newcommand{\ShowPartially}[1]{%
\pgfkeys{/hide letter/.cd,#1}%
\ifhideletterinitial
\setcounter{letterpos}{0}%
\xdef\HideLetterWord{\pgfkeysvalueof{/hide letter/word}}%
\edef\temp{\noexpand\pgfparserparse{letterhide}\HideLetterWord;}%
\temp
\xdef\HideLetterNum{\number\value{letterpos}}%
\pgfmathsetmacro{\myperm}{randompermutation(\HideLetterNum)}%
\xdef\HideLetterPerm{\myperm}%
\hideletterinitialfalse
\fi
\pgfmathsetmacro{\mysublist}{take("\HideLetterPerm",\pgfkeysvalueof{/hide letter/n})}%
\setcounter{letterpos}{0}%
\edef\temp{\noexpand\pgfparserparse{letterhide}\HideLetterWord;}%
\temp
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\pgfmathsetseed{123}
\ShowPartially{initial,n=2,word=Murmeltier} 

\ShowPartially{n=3}

\ShowPartially{n=4}

\ShowPartially{n=5}

\ShowPartially{n=8}

\pgfmathsetseed{42}
\ShowPartially{initial,n=5,word=Amsterdam}  
\end{document}

And this is an ocgx2 version thereof.

\documentclass{article}
\usepackage{ocgx2}
\usepackage{pgf}
\usepgfmodule{parser}
\renewcommand*\familydefault{\sfdefault}
\makeatletter
%membership test    
\pgfmathdeclarefunction{memberQ}{2}{%
  \begingroup%
    \edef\pgfutil@tmpb{0}%memberQ({\lstPast},\inow)
    \edef\pgfutil@tmpa{#2}%
    \expandafter\pgfmath@member@i#1\pgfmath@token@stop
    \edef\pgfmathresult{\pgfutil@tmpb}%
    \pgfmath@smuggleone\pgfmathresult%
  \endgroup}
\def\pgfmath@member@i#1{%
    \ifx\pgfmath@token@stop#1%
    \else
      \edef\pgfutil@tmpc{#1}%
      \ifx\pgfutil@tmpc\pgfutil@tmpa\relax%
      \gdef\pgfutil@tmpb{1}%
      \fi%
      \expandafter\pgfmath@member@i
    \fi}  
\pgfmathdeclarefunction{randompermutation}{1}{%
\begingroup%          
\c@pgf@counta=0%
\edef\pgfutil@tmpa{0}%
\loop
\advance\c@pgf@counta by1%
\edef\pgfutil@tmpa{\pgfutil@tmpa,\the\c@pgf@counta}%
\ifnum\c@pgf@counta<#1\relax
\repeat
\loop
\advance\c@pgf@counta by-1%
\pgfmathtruncatemacro{\pgfutil@tmpb}{1+rnd*\c@pgf@counta}%
\pgfmathtruncatemacro{\pgfutil@tmpc}{{\pgfutil@tmpa}[\pgfutil@tmpb]}%
\ifnum\c@pgf@counta=\numexpr#1-1\relax
\edef\pgfmathresult{\pgfutil@tmpc}%
\else
\edef\pgfmathresult{\pgfmathresult,\pgfutil@tmpc}%
\fi
\edef\pgfutil@tmpd{\pgfutil@tmpa}%
\edef\pgfutil@tmpa{0}%
\pgfutil@for\my@item:={\pgfutil@tmpd}\do{%
\unless\ifnum\pgfutil@tmpc=\my@item
\unless\ifnum\my@item=0\relax
\edef\pgfutil@tmpa{\pgfutil@tmpa,\my@item}%
\fi\fi}%
\ifnum\c@pgf@counta>0\relax
\repeat
\pgfmath@smuggleone\pgfmathresult%
\endgroup}
\pgfmathdeclarefunction{take}{2}{%
\begingroup%
\c@pgf@counta=0%
\pgfutil@for\my@item:={#1}\do{%
\advance\c@pgf@counta by1%
\ifnum\c@pgf@counta<#2\relax
\ifnum\c@pgf@counta=1\relax
\edef\pgfmathresult{\my@item}%
\else
\edef\pgfmathresult{\pgfmathresult,\my@item}%
\fi\fi}%
\pgfmath@smuggleone\pgfmathresult%
\endgroup}
\makeatother    
\newif\ifhideletterinitial
\hideletterinitialfalse
\pgfkeys{/hide letter/.cd,initial/.is if=hideletterinitial,n/.initial=1,
word/.initial=Rome}
\newcounter{letterpos}
\pgfparserdef{letterhide}{all};{\pgfparserswitch{final}}% 
\pgfparserdefunknown{letterhide}{all}%
{\stepcounter{letterpos}%
\unless\ifhideletterinitial
\pgfmathtruncatemacro{\itest}{memberQ({\mysublist},\number\value{letterpos})}%
\ifnum\itest=1\relax
\pgfparserletter
\else
\phantom{\pgfparserletter}%
\fi
\fi}% \pgfparserletter
\pgfparserset{letterhide/silent=true}%
\newcommand{\ShowPartially}[1]{%
\pgfkeys{/hide letter/.cd,#1}%
\ifhideletterinitial
\setcounter{letterpos}{0}%
\xdef\HideLetterWord{\pgfkeysvalueof{/hide letter/word}}%
\edef\temp{\noexpand\pgfparserparse{letterhide}\HideLetterWord;}%
\temp
\xdef\HideLetterNum{\number\value{letterpos}}%
\pgfmathsetmacro{\myperm}{randompermutation(\HideLetterNum)}%
\xdef\HideLetterPerm{\myperm}%
\hideletterinitialfalse
\fi
\pgfmathsetmacro{\mysublist}{take("\HideLetterPerm",\pgfkeysvalueof{/hide letter/n})}%
\setcounter{letterpos}{0}%
\edef\temp{\noexpand\pgfparserparse{letterhide}\HideLetterWord;}%
\temp
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\pgfmathsetseed{123}

\edef\iloop{2}\hfill\loop
\actionsocg[onmouseall]{}{,,ocg\iloop,}{,,,ocg\iloop}{\iloop}\ 
\edef\iloop{\the\numexpr\iloop+1}%
\ifnum\iloop<11\relax
\repeat


\ShowPartially{initial,n=1,word=Murmeltier}\par 

\edef\iloop{2}\loop
\begin{ocg}{OCG 2}{ocg\iloop}{0}
\ShowPartially{n=\iloop}
\end{ocg}\par
\edef\iloop{\the\numexpr\iloop+1}%
\ifnum\iloop<11\relax
\repeat
\end{document}

When viewed with Acrobat reader, this shows numbers from 1 to 10, and if you click on one of these numbers, the corresponding subset of letters shows up. (I have no idea how one can upload an illustration here.)

Toto, we're not in Kansas, or I have a feeling this is not kids game anymore! — Maesumi, May 01 '20 at 12:10
Thanks! By the way how do we handle spaces, for example if answer is "New York" it comes out as "NewYork". As is I can replace the spaces with -. — Maesumi, May 02 '20 at 23:05
@Maesumi As usual in LaTeX, a space can be obtained width \ (backslash-space) as in \ShowPartially{initial,n=10,word=New\ York\ City}. — , May 02 '20 at 23:08

Making letters of a word appear in random order

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