Create a rectangle with the same width as another, fitted rectangle?

Question

The title says it all. I have a few nodes, and created a fitting rectangle. Now, I'd like to create another rectangle at exactly the bottom of it, so it would look like one big rectangle has been split in two.

Answer 1

Yes there is also the possibility to use multi-part nodes with rectangle.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes.multipart} 
\begin{document}

\begin{tikzpicture}[every node/.style={draw, anchor=text, rectangle split, rectangle split parts=2}]
\node {Some text \nodepart{second} more }; 
\end{tikzpicture}
\end{document} 

Answer 2

You can calculate the size of the first rectangle node as follows and use it to draw the second one. One issue is the outer sep of the first node which is normally .5\pgflinewidth, i.e. to place the anchor at the outer edge of the node border, not in the middle of it. This has to be compensated and is error prone if the line width is changed between the nodes.

Note that there is also the possibility to use multi-part nodes. There is one for a circle node, but I'm not sure for rectangle ones.

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}
\begin{tikzpicture}
   \node [draw] (A) {Some text};
   \path let \p1 = (A.south west), \p2 = (A.north east) in
    node [draw,minimum width=\x2-\x1-\pgflinewidth,minimum height=\y2-\y1-\pgflinewidth,below right]
        at ([yshift={\pgflinewidth}]A.south west) {more};
\end{tikzpicture}
\end{document}

Answer 3

Given that you're already using the fit library, you can just use that to get your new rectangle. If you're willing to set outer sep=0pt on your original fitting node then you can fit the new rectangle to the old one plus some random coordinate to set the height, or to the southern anchors of the old one. If you're not willing to set the outer sep on the original node, then simply fit the new node to the same nodes as the original one plus an extra one to make it bigger. In the following, I've made the rectangles different colours so it's obvious what is actually being drawn, but if they are the same colour you won't notice that.

\documentclass{article}
% \url{http://tex.stackexchange.com/q/20998/86}
\usepackage{tikz}
\usetikzlibrary{fit}

\begin{document}
\begin{tikzpicture}[inner node/.style={draw,dashed,blue,text=black},outer node/.style={draw,ultra thick}]
\node[inner node] (a) at (0,0) {a};
\node[inner node] (b) at (2,3) {b};
\node[inner node] (c) at (3,2) {c};
\node[fit=(a) (b) (c),outer node,outer sep=0pt,purple] (d) {};
\path (d.south) ++(0,-5) coordinate (e) {};
\node[pink,outer node,inner sep=0pt,fit=(e) (d.south east) (d.south west)] {};
\begin{scope}[xshift=5cm]
\node[inner node] (a) at (0,0) {a};
\node[inner node] (b) at (2,3) {b};
\node[inner node] (c) at (3,2) {c};
\node[fit=(a) (b) (c),outer node,outer sep=0pt,purple] (d) {};
\path (d.south) ++(0,-5) coordinate (e) {};
\node[pink,outer node,inner sep=0pt,fit=(e) (d)] {};
\begin{scope}[xshift=5cm]
\node[inner node] (a) at (0,0) {a};
\node[inner node] (b) at (2,3) {b};
\node[inner node] (c) at (3,2) {c};
\node[fit=(a) (b) (c),outer node,purple] (d) {};
\path (d.south) ++(0,-5) coordinate (e) {};
\node[pink,outer node,fit=(a) (b) (c) (e)] {};
\end{scope}
\end{scope}
\end{tikzpicture}
\end{document}

Result: