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Relatively simple problem: I want to use macros to define substructures of a tree. In the following example for illustration, I want to define some children (left and right) to be used several times in a tree. 

\documentclass{article} \usepackage{tikz} \begin{document} \begin{tikzpicture} \newcommand{\leftchildren}{% child{node[circle,draw] {l}} child{node[circle,draw] {l}} % }% \newcommand{\rightchildren}{% child{node[circle,draw] {r}} child{node[circle,draw] {r}} % }% \node[circle,draw] (root) {} \leftchildren \rightchildren; \end{tikzpicture} \end{document}

The problem is

  • Without the label (root) it does not even compile (Why?)

  • The macros are not expanded on the same level: the right children become children of the left children

  • Using more macros, or nesting them, makes it worse.

This is a very simplified version of what I want to do. Often I want to be able to add other children by hand (without using macro). I also would like to be able to define entire subtrees as macros, for example a long chain, as a macro.

I think there is a problem with the expansion of the macros, but I was not able to figure it out myself. Help please.

Cheers, Oliver

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  • Your suspicion is right, the macros should be expanded before node starts to read. From the manual: When a node operation like node {X} is followed by child, TikZ starts counting the number of child nodes that follow the original node {X}. For this, it scans the input and stores away each child and its arguments until it reaches a path operation that is not a child. Commented Jun 13, 2012 at 11:41
  • And indeed, \expandafter\leftchildren\rightchildren does what I would expect your code to produce. Commented Jun 13, 2012 at 11:45
  • Which suggests to me that the right strategy would be to have a "tree building" command which expanded all the pieces before feeding it to TikZ. How complicated are your trees? Are there any macros in, say, the node texts? In the example one could do \edef\children{\leftchildren\rightchildren} but that wouldn't work if there was fancy stuff going on. Commented Jun 13, 2012 at 11:47
  • Oh, and for your first comment: the root node needs to have a name otherwise there's no way for TikZ to connect it to its children. The root node is processed before TikZ knows that it is constructing a tree so it doesn't know that that node is going to be used later and therefore it doesn't know to assign it a name automatically. With the internal nodes, TikZ knows that they are part of a tree so knows to give them names (if they don't already have them). Commented Jun 13, 2012 at 11:50
  • (And you now have enough reputation to post pictures. That's always helpful.) Commented Jun 13, 2012 at 11:50

4 Answers 4

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This is similar to

macro for empty nodes in tikz-qtree

You need to pre-expand macros so the tikz parser sees them:

enter image description here

\documentclass{article} \usepackage{tikz} \begin{document} \begin{tikzpicture} \node[circle,draw] (root) {} child{node[circle,draw] {l}} child{node[circle,draw] {l}} child{node[circle,draw] {r}} child{node[circle,draw] {r}}; \end{tikzpicture} aaaaaaaaaaaaaaaaa \begin{tikzpicture} \newcommand{\leftchildren}{% child{node[circle,draw] {l}} child{node[circle,draw] {l}} % }% \newcommand{\rightchildren}{% child{node[circle,draw] {r}} child{node[circle,draw] {r}} % }% \node[circle,draw] (root) {} \leftchildren \rightchildren; \end{tikzpicture} bbbbbbbbbbbbbbbbbbbbbbbbbbbb \makeatletter \let\mypgfutil@ifnch\pgfutil@ifnch \def\pgfutil@ifnch{% \let\x@next\@empty \ifx\pgfutil@let@token\leftchildren\let\pgfutil@let@token c\let\x@next\expandafter\fi \ifx\pgfutil@let@token\rightchildren\let\pgfutil@let@token c\let\x@next\expandafter\fi \x@next\mypgfutil@ifnch} \makeatother \newcommand{\leftchildren}{% child{node[circle,draw] {l}} child{node[circle,draw] {l}} % }% \newcommand{\rightchildren}{% child{node[circle,draw] {r}} child{node[circle,draw] {r}} % }% \begin{tikzpicture} \node[circle,draw] (root) {} \leftchildren \rightchildren; \end{tikzpicture} \end{document}
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  • Thank you very much David. That is exactly what I suspected, but I was not able to achieve this expansion. To be honest, I understand almost nothing of the solution code you use to force the expansion ;-). But that is also not that important. I just need to understand what I need to do for more macros. I guess just adding a new line for each macro? Cheers, Commented Jun 13, 2012 at 12:59
  • yes the c in that line is the first token of the expansion, first letter of child in each case here. (It would be possible to rejig things so you didn't need to do that but....) Commented Jun 13, 2012 at 13:06
  • OK, I see. That is no problem. By the way, will this solution also work when the macros have parameters? Commented Jun 13, 2012 at 13:44
  • probably it'll work, if my understanding of what tikz is doing here is correct. I have almost no knowledge of tikz though:-) Commented Jun 13, 2012 at 14:09
  • Just an update from my side. David's solution also works for macros with parameters. Great! Thanks Ahmed for your suggestion, but I understand even less ;-). Never mind, I can live with the c character. (Even though it is easy to forget to change when you change the macro, happened already). Oliver Commented Jun 14, 2012 at 9:05
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The character c is required to be always present in Master David Carlisle's approach. Here is an approach that I sometimes use.

\documentclass{article} \usepackage{tikz} \makeatletter \newcommand*\tikzcommands{% % Collect your tikz commands here, otherwise they will be expanded % prematurely: \do\begin\do\end\do\coordinate\do\path\do\draw\do\node } \def\xtikzpicture{\@ifnextchar'{\@firstoftwo{\xtikz@picture{00}}}% {\xtikz@picture{01}}} \def\xtikz@picture#1#2\end#3{% \def\reserved@a{#3}\def\reserved@b{xtikzpicture}% \ifx\reserved@a\reserved@b \def\endxtikzpicture{}% \end{xtikzpicture}% \else \@latexerr{Environment 'xtikzpicture' badly ended}\@ehd \fi \let\this@relax\relax \def\reserved@a##1\this@relax{}% \if#1\expandafter\reserved@a\fi \begingroup \def\do##1{\let##1\relax}\tikzcommands \protected@edef\x{\endgroup \begin{tikzpicture}#2\end{tikzpicture}% }\x \this@relax } \makeatother \def\leftchildren{% child{node[circle,draw] {left}} child{node[circle,draw] {left}} } \def\rightchildren{% child{node[circle,draw] {\textcolor{blue}{right}}} child{node[circle,draw] {\textcolor{blue}{right}}} } \begin{document} \begin{xtikzpicture}' % ignored xx \end{xtikzpicture} \begin{xtikzpicture}[level distance=10mm, every node/.style={fill=red!40,circle,inner sep=1pt}] % Maybe someone can tell me why the circle on 'root' has no effect: \node {root} [grow'=up,circle,draw] \leftchildren \rightchildren child {node {parent} child {node {child}} child {node {child}} }; \end{xtikzpicture} \end{document}

enter image description here

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With forest, you can easily specify complex sub-trees, format them in different ways and mix explicit and automatic node creation within your tree. And you can do all this very concisely and without needing to worry about expansion issues. (At least, usually not.)

For example:

\documentclass[tikz,border=5pt,multi]{standalone} \usepackage{forest} \begin{document} \forestset{ my circle/.style={circle, draw}, my node/.style={draw}, left children/.style={ repeat=2{prepend={[l, my circle]}} }, right children/.style={ repeat=2{append={[r, my circle]}} }, complex children/.style={ before typesetting nodes={for descendants={my node}}, append={[+1, left children, delay={for children={right children}}, before typesetting nodes={for tree={blue, edge={blue}}}, insert after={[+2, repeat=3{prepend={[p, for tree={green, edge={green}}[p]]}, append={[a, for tree={red, edge={red}}]}}]}]} } } \begin{forest} [, my circle, left children, right children [, my circle, complex children] ] \end{forest} \end{document}

The style my circle just sets the node shape to a circle and draws it.

The styles left children and right children create 2 left and 2 right children relative to the current node with the my circle style.

The style complex children creates a sub-tree consisting of a left side (+1) and right side (+2). By default, all nodes in this sub-tree use the my node style which draws a box around the default, rectangular node shape. The left side is coloured blue and the root node uses the my node style but its children use the my circle style because these are created with left children and right children. The right side is not initially coloured but the children on this side are. The 3 left children are green and their children are also green. The 3 right children are red. And so on.

Obviously, you can define simpler or more complex structures and styles as required.

automated node structures using <code>forest</code> styles

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You can also force expansion of your macro with \edef :

\edef\tmp{\leftchildren \rightchildren} \node[circle,draw] (root) {} \tmp;
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