# Vertical alignment in TikZ matrix

I am using a TikZ matrix to make a diagram where the entries in a row vary considerably in size:

\documentclass{article}

\usepackage{tikz,amsmath}
\usetikzlibrary{matrix}

\begin{document}

\newcommand{\RandomDots}{%
\begin{tikzpicture}
\foreach \x in {0.1, 0.3,...,1}
\foreach \y in {0.1, 0.3,...,1}
{
\pgfmathrandominteger{\r}{1}{5}
}
\end{tikzpicture}
}

\begin{tikzpicture}[%
feature box/.style = {rectangle, draw, anchor=center},
]

\matrix [
matrix of math nodes,
column sep = 1cm,
row sep = 0.1cm
]
{
|(a)| a & \node [feature box] (f1) {\RandomDots}; \\
|(b)| b & \node [feature box] (f2) {\RandomDots}; \\
};

\draw [->] (a) -- (f1);
\draw [->] (b) -- (f2);
\end{tikzpicture}
\end{document}


The resulting image looks like this:

However, I would like the connections to be horizontal/the box from \RandomDots to be vertically aligned with the letters in the first column.

Does anyone know of a way to do this?

-
Adding nodes={anchor=east} (or west) to your matrix can help in this specific case. –  percusse Jun 6 '12 at 14:04

\draw [->] (a) -- (f1.west|-a);