title: Tikz: horizontal centering of group of nodes
body: <p>I need to align each row of the graph to the center. I am trying to do it with xshift. Here the code:</p>
  
  <pre><code>    \begin{tikzpicture}[node distance=1.5cm, auto, text centered]
      \tikzstyle{every node}=[draw,ball];
      \begin{scope}[xshift=1.5cm]
          \node (A) {A};
          \node [right of=A] (B) {B};
          \node [right of=B] (C) {C};
          \node [right of=C] (D) {D};
      \end{scope}
      \begin{scope}[yshift=-1.5cm]
          \node (AB) {AB};
          \node [right of=AB] (AC) {AC};
          \node [right of=AC] (AD) {AD};
          \node [right of=AD] (BC) {BC};
          \node [right of=BC] (BD) {BD};
          \node [right of=BD] (CD) {CD};
      \end{scope}
      \begin{scope}[yshift=-3cm,node distance=2cm,xshift=1cm]
          \node (ABC) {ABC};
          \node [right of=ABC] (ABD) {ABD};
          \node [right of=ABD] (ACD) {ACD};
          \node [right of=ACD] (BCD) {BCD};
      \end{scope}
      \begin{scope}[xshift=4cm, yshift=-4.5cm, node distance=2cm]
          \node (ABCD) {ABCD};
      \end{scope}
  \end{tikzpicture}
  </code></pre>
  
  <p>Is there any other way to do it? Do not like to change xshift values every time.</p>