Ifthenelse - Comparing strings (one inferior to another)

Question

This topic is following my previous question, which was marvelously answered by BambOo yesterday.

Now for a step beyond into this project.

Let's admit I want to put a list of letters (or words) on a 6 columns grid and stylize them depending on their content.

In the following example, I displayed a simple alphabet, and a [count=\i] into the loop, but I'd like to be able to compare directly the node content, i.e. something like ifthenelse(\l<"J", nodeone, nodetwo). Is there any simple way to do that?

\documentclass[a4paper, 11pt]{article}

\usepackage[utf8]{inputenc}
\usepackage[french]{babel}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{tikz}
\usetikzlibrary{shapes}

\usepackage{ifthen}


\begin{document}


\begin{center}
\begin{tikzpicture}


\tikzstyle{nodeone}=[circle, fill=cyan!50!yellow,text=purple,opacity=1,minimum height=30]
\tikzstyle{nodetwo}=[regular polygon,regular polygon sides=5, fill=orange!50!red,text=cyan,opacity=1,minimum height=30]
\tikzstyle{nodethree}=[star,star points=7,star point ratio=0.8, fill=red!50!blue,text=orange,opacity=1,minimum height=30]



\def\LX{2} \def\LY{3} \def\ncol{6} % dimensions of the grid
\def\firstlim{8} \def\secondlim{17}

\foreach \l [count=\i from 0] in {A,...,Z}
    {
    \pgfmathsetmacro{\nodestyl}
        {
        ifthenelse(\i<\firstlim,"nodeone",
            ifthenelse(\i<\secondlim,"nodetwo","nodethree")
        }%

    \pgfmathtruncatemacro\result{\i/\ncol}
    \node[\nodestyl] at ({Mod(\i,\ncol)*\LX},-\result*\LY) {\sf \Large \textbf{\l}};
    }


\end{tikzpicture}
\end{center}

\end{document}

I already looked into etoolbox to find something that could help, and I found a way to test if strings are equal : \expandafter\ifstrequal\expandafter{\l}{A}{\nodeone}{nodetwo}, but not yet a way to test if string1 is inferior to string2.

Answer 1

You can do such comparisons with \pdf@strcmp from the pdftexcmds package. I've tested the following code with pdfTeX, XeTeX and LuaTeX—all of these support the command. \pdf@strcmp expands to -1, 0 or 1 depending on whether the first string compares strictly less, equal to or strictly greater than the second string (ASCII is certainly supported; for the rest, I don't know—this might be engine-dependent).

Don't use \tikzstyle, it is obsolete; instead, use \tikzset or the optional argument of tikzpicture (see below). Prefer using the font option to define the font to be used in TikZ nodes and never use \sf with LaTeX: it is a plain TeX font command, not LaTeX. Better use \sffamily or \textsf—these are LaTeX font selection commands.

\documentclass[tikz, border=1mm]{standalone}
\usetikzlibrary{shapes}
\usepackage{pdftexcmds}

\makeatletter
% Expand #1 once before comparing it to #2
\newcommand*{\mystrcmp}[2]{%
  \expandafter\pdf@strcmp\expandafter{#1}{#2}%
}
\makeatother

\begin{document}
\begin{tikzpicture}[
  nodeone/.style={circle, fill=cyan!50!yellow,text=purple,opacity=1,
                  minimum height=30},
  nodetwo/.style={regular polygon,regular polygon sides=5,
                  fill=orange!50!red,text=cyan,opacity=1,minimum height=30},
  nodethree/.style={star,star points=7,star point ratio=0.8,
                    fill=red!50!blue,text=orange,opacity=1,minimum height=30},
  ]

% Dimensions of the grid
\newcommand*{\LX}{2} \newcommand*{\LY}{3} \newcommand*{\ncol}{6}

\foreach \l [count=\i from 0] in {A,...,Z}
  {
    \edef\myNodestyle{%
      \ifnum\mystrcmp{\l}{I}=-1   % space intended
        nodeone%
      \else
        \ifnum\mystrcmp{\l}{R}=-1 % space intended
          nodetwo%
        \else
          nodethree%
        \fi
      \fi
    }

    \pgfmathtruncatemacro{\result}{\i/\ncol}
    \node[\myNodestyle, font=\sffamily\Large\bfseries]
      at ({Mod(\i,\ncol)*\LX}, -\result*\LY) {\l};
  }
\end{tikzpicture}
\end{document}