[Tex/LaTex] simpler way of drawing relation maps

tikz-pgf

For an example relation R: A -> B, I have the following TikZ code:

\documentclass[tikz]{standalone}
\usepackage{tikz}
\usetikzlibrary{shapes,backgrounds,decorations.text,patterns}
\usetikzlibrary{plotmarks}

\begin{document}
\begin{tikzpicture}
  \begin{scope}[mark=*,mark size=1pt]
% sets A & B
  \draw (0,0) node[ellipse, minimum height=50pt,minimum width=30pt,draw,label=above:A]{};
  \draw (2,0) node[ellipse, minimum height=50pt,minimum width=30pt,draw,label=above:B]{};
% draw line and label origin a to c
  \draw[->] plot coordinates {(0,10pt)} (0,10pt) node[above]{a} -- (1.9,16pt);
% add end point
  \node at (2,16pt) {\pgfuseplotmark{*}};
% add end label
  \node[above] at (2,16pt) {c};
% draw line and label origin a to e
  \draw[->] plot coordinates {(0,10pt)} (0,10pt) node[above]{a} -- (1.9,-15pt);
% add end point
  \node at (2,-15pt) {\pgfuseplotmark{*}};
% add end label
  \node[above] at (2,-15pt) {e};
% draw line and label origin b to d
  \draw[->] plot coordinates {(0,-10pt)} (0,-10pt) node[above]{b} -- (1.6,2pt);
 % add end point
  \node at (1.7,2pt) {\pgfuseplotmark{*}};
% add end label
  \node[above] at (1.7,2pt) {d};


\end{scope}
\end{tikzpicture}
\end{document}

Produces:

enter image description here

Is there a simpler way of accomplishing this in TikZ? It seems like a lot of work.

Best Answer

No doubt requires adjustment since I'm not aware of the applicable criteria:

\documentclass[tikz,border=5pt]{standalone}
\usetikzlibrary{shapes,positioning,fit,calc}

\begin{document}
  \begin{tikzpicture}
    [
      group/.style={ellipse, draw, minimum height=50pt, minimum width=30pt, label=above:#1},
      my dot/.style={circle, fill, minimum width=2.5pt, label=above:#1, inner sep=0pt}
    ]
    \node (a) [my dot=a] {};
    \node (b) [below=of a, my dot=b] {};
    \node (c) [right=50pt of a, my dot=c] {};
    \node (e) [below=of c, my dot=e] {};
    \node (d) [xshift=-2.5pt, my dot=d] at ($(c)!1/2!(e)$) {};
    \foreach \i/\j in {a/c,a/e,b/d}
      \draw [->, shorten >=2pt] (\i) -- (\j);
    \node [fit=(a) (b), group=A] {};
    \node [fit=(d) (c) (e), group=B] {};
  \end{tikzpicture}
\end{document}

groups

This uses styles to minimise repetition of code. In particular, it uses styles which use an argument (#1) for the label. It also uses the fit library for the ellipses and the positioning and calc libraries to help in specifying locations. This makes it possible to save quite a lot of code. Finally, a loop is used to draw the arrows although this might not really be worth the trouble if you only have 3 arrows to draw - it really comes into its own, though, if you have something more like 30.

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