Defining node inside curly braces

Question

I am trying to define a node inside a curly braces {}:

\documentclass{article}

\usepackage{tikz}
\usepackage{tikz-qtree}

\begin{document}

\begin{tikzpicture}
\Tree [.CP \node(y){here}; [.C$'$ C [.TP \edge[roof]; {Some text \node(x){here};} ]]]
\end{tikzpicture}

\end{document}

I need to define the node x inside the {} environment since I want tikz-qtree to treat the string 'Some text here' as a single unit. However, if I place the semicolon after the first or second closing bracket, it does not work.

Answer 1

Since the text inside the roofed node is a node itself internally and you can't embed nodes within nodes, you need to attack this problem in a slightly different way. The basic idea is to make the parent node of the roofed node the named node instead. Then if you want to show, e.g. an arrow from each of the nodes you have to offset the starting point of the arrow relative to the parent node. Here's an example:

\documentclass{article}

\usepackage{tikz}
\usepackage{tikz-qtree}

\begin{document}

\begin{tikzpicture}
\Tree [.CP \node(y){here}; [.C$'$ C [.\node(x){TP}; \edge[roof];  {Some text here} ]]]
\draw [->] (x.south)++(.9,-1) to[out=-90,in=-90,looseness=2] (y.south); 
\end{tikzpicture}

\end{document}

An alternative method (which is perhaps a bit simpler) is to define the roof text itself as a node, and then just use the [xshift] parameter to shift the start point of the arrow to the desired spot:

\documentclass{article}

\usepackage{tikz}
\usepackage{tikz-qtree}

\begin{document}

\begin{tikzpicture}
\Tree [.CP \node(y){here}; [.C$'$ C [.TP \edge[roof];  \node(x){Some text here}; ]]]
\draw [->] ([xshift=2.5em]x.south) to[out=-90,in=-90,looseness=2] (y.south); 
\end{tikzpicture}

\end{document}

Answer 2

Just in case it had escaped anybody's notice, I tend to prefer forest when drawing trees.

This solution does not require manually repeating the word 'here' or manually adjusting the positioning of the start of the arrow. It is based on an example from page 20 of the manual, though I may have mangled it a little.

• triangle is used for the roof
• a style, move={}{} is defined which takes 2 arguments: the first specifies the node to which the content should be copied; the second specifies additional text to add to the current node.

I'm assuming that you may not want to do exactly this, so this is more by way of illustration than a ready-to-use solution. In the example you gave, you would put move={<specification of target node>}{Some text} and you would specify the content of the source node as here.

The source node would then end up containing Some text here, the target node would end up containing here and an arrow would be drawn between a point just below here in the source node and one just below here in the target node.

I've used a 'relative node walk' to specify the target node. However, you could equally add , name=target to your target node and then just put move={target}{Some text}, which is probably simpler in most cases. I've added this alternative as commented code in the tree to demonstrate the idea.

\documentclass[tikz,border=5pt]{standalone}
\usepackage{forest}
\begin{document}
  \newlength{\sourcetextaddwidth}
  \begin{forest}
    for tree={
      parent anchor=south,
      child anchor=north,
      fit=rectangle
    },
    move/.style n args=2{% page 20 of forest manual
      before typesetting nodes={
        TeX={
          \settowidth{\sourcetextaddwidth}{#2}
        },
        #1.content={##1},
        content={#2 ##1},
        tikz={
          \draw[->] (.south) +(.5\sourcetextaddwidth,0) to [out=south west, in=south] (#1);
        },
      },
    },
    [CP
      [this is the target node to which text will be moved%, name=target
      ]
      [C$'$
        [C
        ]
        [TP
          [here, triangle, move={!r1}{Some text}% move={target}{Some text}
          ]
        ]
      ]
    ]
  \end{forest}
\end{document}