Shifted edge labels in tikzpictures in nodes side by side

Question

I'm trying to make two graphs and place them side by side and place edge labels over edges in the two graphs (as can be seen in the picture), but I am not successful in the second graph. My approach is to create two nodes in one tikzpicture nad place another two tikzpictures (the graphs itself) in these nodes. Here is my code:

\documentclass[12pt,a4paper]{article}
\usepackage[czech]{babel}
\usepackage{tikz}
\usetikzlibrary{positioning,shapes,shadows,arrows,decorations.pathreplacing, snakes}

\begin{document}
    \begin{tikzpicture}
    \tikzstyle{every node}=[circle, minimum size=0pt, inner sep=0pt, outer sep=0pt, fill=white],
    \tikzstyle{vertex}=[circle, minimum size=4pt, inner sep=0pt, fill=orange]
        \node(graph) at (0,1) {
            \begin{tikzpicture}[font=\footnotesize, thick]
            \begin{scope}
                \node[vertex] (root)    at (4,  5) {};
                \node[vertex] (o)       at (4,  4) {};
                \node[vertex] (oc)      at (4,  3) {};
                \node[vertex] (a)       at (5,  4) {};

                \foreach \xfrom/\xto/\xlabel in {
                    root/o/o, o/oc/c,
                    root/a/a} {
                    \draw (\xfrom) to node[pos=0.5]{\xlabel} (\xto);
                };
            \end{scope}             
            \end{tikzpicture}
        };

        \node[right = of graph] (graph2) {
            \begin{tikzpicture}[font=\footnotesize, thick]
            \begin{scope}
                \node[vertex] (root)    at (4,  5) {};          
                \node[vertex] (o)       at (4,  4) {};
                \node[vertex] (oc)      at (4,  3) {};          
                \node[vertex] (a)       at (5,  4) {};

                \foreach \xfrom/\xto/\xlabel in {
                    root/o/o, o/oc/c} 
                {
                    \draw (\xfrom) to node[pos=0.5]{\xlabel} (\xto);
                };
                \foreach \xfrom/\xto/\xlabel in {
                    root/a/a} 
                {
                    \draw (\xfrom) to node[midway]{\xlabel} (\xto);
                };
            \end{scope}             
            \end{tikzpicture}
        };  
    \end{tikzpicture}
\end{document}

My result is as follows:

What am I doing wrong or what am I missing? I would appreciate any suggestions. (I need to do it this way because of exact positioning of the graphs and because of additional arrows that will connect these graphs.)

EDIT: Actually, I need to make an arrow between the two graphs:

\documentclass[12pt,a4paper]{article}
\usepackage[czech]{babel}
\usepackage{tikz}

\usetikzlibrary{positioning,shapes,shadows,arrows,decorations.pathreplacing, snakes}

\begin{document}
\begin{tikzpicture}
    \tikzstyle{every node}=[circle, minimum size=0pt, inner sep=0pt, outer sep=0pt, fill=white],
    \tikzstyle{vertex}=[circle, minimum size=4pt, inner sep=0pt, fill=orange]
        \node(graph) at (0,1) {
            \begin{tikzpicture}[font=\footnotesize, thick]
            \begin{scope}
                \node[vertex] (root)    at (4,  5) {};
                \node[vertex] (o)       at (4,  4) {};
                \node[vertex] (oc)      at (4,  3) {};
                \node[vertex] (a)       at (5,  4) {};

                \foreach \xfrom/\xto/\xlabel in {
                    root/o/o, o/oc/c,
                    root/a/a} {
                    \draw (\xfrom) to node[pos=0.5]{\xlabel} (\xto);
                };
            \end{scope}             
            \end{tikzpicture}
        };

        \node[right = of graph] (graph2) {
            \begin{tikzpicture}[font=\footnotesize, thick]
            \begin{scope}
                \node[vertex] (root)    at (4,  5) {};          
                \node[vertex] (o)       at (4,  4) {};
                \node[vertex] (oc)      at (4,  3) {};          
                \node[vertex] (a)       at (5,  4) {};

                \foreach \xfrom/\xto/\xlabel in {
                    root/o/o, o/oc/c} 
                {
                    \draw (\xfrom) to node[pos=0.5]{\xlabel} (\xto);
                };
                \foreach \xfrom/\xto/\xlabel in {
                    root/a/a} 
                {
                    \draw (\xfrom) to node[midway]{\xlabel} (\xto);
                };
            \end{scope}             
            \end{tikzpicture}
        };  

        \begin{scope}[segment amplitude=4]
        \draw[snake=triangles] (graph) -- (graph2);
        \end{scope}
    \end{tikzpicture}
\end{document}

I'm not sure if this is possible with pic...

OK, so my approach is completely wrong? There is no way how to make my example working? — Frimlik, May 03 '18 at 18:18
There is the pic syntax, but since this is too long for a comment I posted an answer. — , May 03 '18 at 18:25

score 3 · Accepted Answer · 2018-05-03T19:31:26.630

There is the pic syntax allowing one to draw small pictures in a tikzpicture.

\documentclass[12pt,a4paper]{article}
\usepackage{tikz}
\usetikzlibrary{positioning,shapes,shadows,arrows,decorations.pathreplacing, snakes}
%
    \tikzset{every node/.style={circle, minimum size=0pt, inner sep=0pt, outer sep=0pt, fill=white},
    vertex/.style={circle, minimum size=4pt, inner sep=0pt, fill=orange}}

\tikzset{
  mygraph/.pic={\begin{scope}[font=\footnotesize, thick]
                \node[vertex] (root)    at (4,  5) {};
                \node[vertex] (o)       at (4,  4) {};
                \node[vertex] (oc)      at (4,  3) {};
                \node[vertex] (a)       at (5,  4) {};

                \foreach \xfrom/\xto/\xlabel in {
                    root/o/o, o/oc/c,
                    root/a/a} {
                    \draw (\xfrom) to node[pos=0.5]{\xlabel} (\xto);
                };
                \end{scope}
  }
}

\begin{document}
    \begin{tikzpicture}
    \pic (graph) {mygraph};
    \pic at (3,0) (graph2) {mygraph};
    \end{tikzpicture}
\end{document}

If you want to change some things, then you can work with parameters. (And please note that \tikzstyle is deprecated.)

EDIT: To reference the nodes inside the pics outside, you just need to add the appropriate prefix, e.g.

\draw[-latex,shorten >=3mm,shorten <=3mm] (grapha) -- (graph2o);

will yield

Explanation: the nodes inside the picture can be referenced as <pic name><node name> such that the node a in the pic named graph becomes grapha. (shorten just shortens the arrow.) Notice that you could also play with nodes and the path picture key, but for this this might be less elegant.

So instead of nested tikzpictures I only add some pics... Nice solution! Thank you very much! — Frimlik, May 03 '18 at 18:30
And regarging the note about tikzstyle - I am a very occasional user of LaTeX, so I'm not very familiar about tikzset. So thank you also for information and warning. — Frimlik, May 03 '18 at 18:32
Is there a way to name the two pics to be able to draw an arrow between them? — Frimlik, May 03 '18 at 19:10
@Frimlik Sure, just do \draw[-latex,shorten >=3mm,shorten <=3mm] (grapha) -- (graph2o);. Explanation: the nodes inside the picture can be referenced as <pic name><node name> such that the node a in the pic named graph becomes grapha. (shorten just shortens the arrow.) Notice that you could also play with nodes and the path picture key, but for this this might be less elegant. — , May 03 '18 at 19:22
I edited question - I need the arrow to be directed from center of the left and to the center of the right graph. — Frimlik, May 03 '18 at 19:55
@Frimlik \path (grapha) -- (graph2o) coordinate[pos=0.2] (start) coordinate[pos=0.8] (end); \draw[snake=triangles,segment amplitude=4] (start) to (end);. Notice that I am not supposed to be doing this. Rather, you are supposed to ask a new question. — , May 03 '18 at 20:05

Shifted edge labels in tikzpictures in nodes side by side

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