Multiple TikZ keys with foreach

Question

Playing around with pgffor, I'm trying to slightly modify an example from the TikZ/pgf manual:

\path \foreach \x/\content/\style in {%
  0/a/draw,
  1/b/{draw,red},
  2/c/{circle,blue},
  3/d/draw%
} {
  node[\style] at (\x,0) {\content}
} ;

Unfortunately, this does not work for nodes with multiple \style options set. TikZ complains with

! Package pgfkeys Error: I do not know the key '/tikz/draw,red' and I am going
to ignore it. Perhaps you misspelled it.

Now, this works perfectly, when I use a comma separated list for some other variable (e.g. \content). So now, my question is: how can I split \style while executing the loop? Obviosly, pgf tries to find one key named draw,red, when it should be looking for two keys instead, namely draw and red.

Is there some clever LaTeX macro that correctly expands the loop variable or tells pgf to expect multiple keys?

Answer 1

Here's another version, not all that different from the previously supplied but combines them in a slightly different way. In effect, it is a bit like defining a dynamic style alias that expands to the given list of options. When a style like red drawing/.style={draw,red} is defined, then calling red drawing executes \tikzset{draw,red} (sort of, actually it's pgfkeys). So we simulate this by defining a key that executes \tikzset on whatever it is passed. So apply style={do,something,and,something,else} will execute \tikzset{do,something,and,something,else}. On its own, this isn't all that useful. But when combined with the /.expand once key handler we can pass it a macro, get that macro expanded once, and then execute the style it contains.

\documentclass{article}
\usepackage{tikz}
\tikzset{%
  apply style/.code={%
    \tikzset{#1}%
  }
}
\begin{document}

\begin{tikzpicture}
\path \foreach \x/\content/\style in {%
  0/a/draw,
  1/b/{draw,red},
  2/c/{circle,draw=blue},
  3/d/draw%
} {
  node[apply style/.expand once=\style] at (\x,0) {\content}
} ;
\end{tikzpicture}
\end{document}

Answer 2

Use indirect styles numbered (perhaps more verbose but flexible):

\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}
  \tikzset{
    s0/.style={draw},
    s1/.style={draw,red},
    s2/.style={circle,draw=blue},
    s3/.style={draw},
  }
  \foreach \x/\content in {%
    0/a,
    1/b,
    2/c,
    3/d%
  } {
    \node[s\x] at (\x,0) {\content};
  };
\end{tikzpicture}
\end{document}

Answer 3

Personally I always use the next method and in a lot of cases I use \protected@edef with LaTeX. With the next method you can use \path node ... node ... ;.

\documentclass{standalone}
\usepackage{tikz}
 % \makeatletter\let\protectededef\protected@edef   not useful here but It' sometimes  
 % interesting
\begin{document}
  \begin{tikzpicture}
    \path 
    \foreach \x/\content/\style in {0/a/draw,
                                    1/b/{draw,red},
                                    2/c/{draw,circle,blue},
                                    3/d/draw}{
  \pgfextra{\edef\tmp{   % or \pgfextra{\protectededef\tmp{
  node[\style] at (\x,0) {\content}}}
  \tmp
  };
  \end{tikzpicture}  
\end{document}

Answer 4

You can stick with your method. With a slight modification, it works.

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  \foreach \x/\content/\style in {%
    0/a/draw,
    1/b/{draw=red},
    2/c/{circle,draw=blue},
    3/d/draw
  }{
    \edef\x{\noexpand\node[\style] at (\x,0) {\content}}\x;
  }
\end{tikzpicture}
\end{document}

And PolGab's solution is:

\documentclass[tikz]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[0/.style=draw,1/.style={draw=red},
    2/.style={circle,draw=blue},3/.style=draw]
  \foreach \x/\content in {0/a, 1/b, 2/c, 3/d}{
    \node[\x] at (\x,0) {\content};
  }
\end{tikzpicture}
\end{document}

EDIT (2012/07/22)

Expanding on Andrew Stacey's solution, here is another one. Using + to list the keys eliminates the need for braces. The code can be generalized to take any symbol in place of +.

\documentclass{article}
\usepackage{tikz}
\makeatletter
\def\replaceplus#1{\xreplaceplus#1+\@nil}
\def\xreplaceplus#1+#2\@nil{%
  \ifcat$\detokenize{#2}$\expandafter\@firstoftwo\else\expandafter\@secondoftwo\fi
  {\unexpanded{#1}}{\xreplaceplus#1,#2\@nil}%
}
\newcommand*\tikzexpanded[2]{%
  \begingroup
  \def\reserved@a##1#1##2##3\@nil{%
    \ifx\@nnil##2\def\x{#2}\else\edef\x{##2{#2}}\fi
  }%
  \reserved@a
    xx{\@iden}x0{\unexpanded}x1{\unexpanded\expandafter}%
    x2{\unexpanded\expandafter\expandafter\expandafter}#1{\@nnil}\@nil
  \edef\x{\expandafter\replaceplus\expandafter{\x}}%
  \edef\x{\endgroup\noexpand\tikzset{\unexpanded\expandafter{\x}}}\x
}
\tikzset{%
  use style/.code={\tikzset{#1}},
  use style expanded/.code={\tikzexpanded{xx}{#1}},
  use style expand once/.code={\tikzexpanded{x1}{#1}},
  use style expand twice/.code={\tikzexpanded{x2}{#1}}
}
\makeatother
\begin{document}
\begin{tikzpicture}
\path \foreach \x/\content/\style in{%
  0/a/draw,
  1/b/draw + red,
  2/c/circle + draw=blue,
  3/d/draw
}{
  node[use style expand once=\style] at (\x,0) {\content}
};
\end{tikzpicture}
\end{document}

Answer 5

I have been using some keys that use the same mechanism as described in the answer by Loop Space. The user syntax is simpler and truthful to the key-value method. It solves more general questions, by expanding a value once, twice or completely before processing it as a key. The example in the question is slightly modified to include an example where expanding twice is necessary.

To answer the question, the following keys set style and expand style once are enough. I include the key expand style twice to solve my modification of the example. I also include the key expand style which is useful when complete expansion is the goal and the number of expansions needed is not known.

You may want to check the minimal examples illustrating these facts in my related answer here.

\documentclass{article}
\usepackage{tikz}
\tikzset{%
  set style/.style={#1},
  expand style/.style={%completely expands the <value> of its argument (using \edef) before processing the result as a <key>
    set style/.expanded={#1}% needs braces around the argument
  },
  expand style once/.style={% expands the <value> of its argument once before processing the result as a <key>
    set style/.expand once={#1}% needs braces around the argument
  },
  expand style twice/.style={% expands the <value> of its argument twice before processing the result as a <key>
    set style/.expand twice={#1}% needs braces around the argument
  }
}
\begin{document}

\begin{tikzpicture}
\def\mystyle{fill=yellow}
\path \foreach \x/\content/\style in {%
  0/a/draw,
  1/b/{draw,red},
  2/c/{circle,draw=blue},
  3/d/\mystyle% \mystyle needs one more expansion after \style has been expanded once.
} {
  node[expand style=\style] at (\x,0) {\content}
} ;
\end{tikzpicture}
\end{document}