% Database decimation process
% Author: Jim Paris
\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{10pt}%
\usepackage{xcolor}
\usepackage{etoolbox}

\usetikzlibrary{decorations}
\usetikzlibrary{decorations.pathreplacing}
\usetikzlibrary{calc}
\usetikzlibrary{arrows}

\newtoggle{quickdecim}
%\toggletrue{quickdecim} % Uncomment this to render more quickly (non-random)

\begin{document}
\begin{tikzpicture}
  \def\levels{4} % 2, 3, or 4
  \pgfmathtruncatemacro{\blocks}{4^(\levels-1)}
  \def\maxrand{99}
  \def\xoffset{1.1}
  \def\yoffset{2.6}
  \pgfmathsetseed{31337}
  \pgfmathsetmacro{\totalwidth}{10}
  \pgfmathsetmacro{\levelheight}{2.4}
  \pgfmathsetmacro{\sampleheight}{0.55}

  \definecolor{lowcolor} {rgb}{0.6,0.6,1}
  \definecolor{highcolor}{rgb}{0.6,1,0.6}

  \tikzstyle{Sample} = [
    draw, anchor=west,
    inner sep=0,
    outer sep=0,
    minimum height=\sampleheight * 1cm,
    font=\small,
    text=black,
  ]

  % make random numbers
  \pgfmathtruncatemacro{\runningrandarray}{random(\maxrand)}
  \foreach \x[count=\xi from 1] in {2,...,\blocks} {
    \let\temprand\runningrandarray
    \pgfmathtruncatemacro{\tempres}{random(\maxrand)}
    \xdef\runningrandarray{\temprand,\tempres}
  }
  \xdef\randarray{{\runningrandarray}}

  % boxes
  \foreach \level in {1,...,\levels} {
    \coordinate (level\level sample0) at
    (\xoffset - \totalwidth / 2,
    \yoffset + \levelheight - \levelheight * \level);
    \pgfmathsetmacro{\avgblocks}{4^(\level-1)}
    \pgfmathsetmacro{\levelblocks}{\blocks / \avgblocks}
    \pgfmathsetmacro{\samplewidth}{\totalwidth/\levelblocks}

    \foreach \i in {1,...,\levelblocks} {
      \iftoggle{quickdecim}{
        % can do this instead of using real samples, for speed
        \xdef\smin{5}
        \xdef\smean{50}
        \xdef\smax{95}
      }{
        % calculate sample values from the randarray
        \pgfmathsetmacro{\smin}{100}
        \pgfmathsetmacro{\smax}{0}
        \pgfmathsetmacro{\samplesum}{0}
        \pgfmathsetmacro{\countfrom}{(\i - 1) * \avgblocks}
        \pgfmathsetmacro{\countto}{\countfrom + \avgblocks - 1}
        \foreach \j in {\countfrom,...,\countto} {
          \pgfmathsetmacro{\tmp}{\samplesum + \randarray[\j] / \avgblocks}
          \xdef\samplesum{\tmp}
          \pgfmathtruncatemacro{\tmp}{min(\smin, \randarray[\j])}
          \xdef\smin{\tmp}
          \pgfmathtruncatemacro{\tmp}{max(\smax, \randarray[\j])}
          \xdef\smax{\tmp}
        };
        \pgfmathtruncatemacro{\tmp}{\samplesum}
        \xdef\smean{\tmp}
      }
      \pgfmathtruncatemacro{\cmin}{(\smin - 1) / (\maxrand - 1) * 100}
      \pgfmathtruncatemacro{\cmean}{(\smean - 1) / (\maxrand - 1) * 100}
      \pgfmathtruncatemacro{\cmax}{(\smax - 1) / (\maxrand - 1) * 100}
      \pgfmathtruncatemacro{\prev}{\i-1}

      \ifnumequal{\level}{1}{
        \node[Sample, xshift=\samplewidth * \prev cm, draw,
        yshift=\sampleheight * -2cm,
        minimum width=\samplewidth cm,
        fill=highcolor!\cmean!lowcolor]
        (level\level samplemax\i) at (level\level sample0) {};
        \coordinate (level\level samplemin\i) at (level\level samplemax\i);
        \coordinate (level\level samplemean\i) at (level\level samplemax\i);
      }{
        \node[Sample, xshift=\samplewidth * \prev cm, draw,
        yshift=\sampleheight * 0cm,
        minimum width=\samplewidth cm,
        fill=highcolor!\cmin!lowcolor]
        (level\level samplemin\i) at (level\level sample0) {\smin};

        \node[Sample, xshift=\samplewidth * \prev cm, draw,
        yshift=\sampleheight * -1cm,
        minimum width=\samplewidth cm,
        fill=highcolor!\cmean!lowcolor]
        (level\level samplemean\i) at (level\level sample0) {\smean};

        \node[Sample, xshift=\samplewidth * \prev cm, draw,
        yshift=\sampleheight * -2cm,
        minimum width=\samplewidth cm,
        fill=highcolor!\cmax!lowcolor]
        (level\level samplemax\i) at (level\level sample0) {\smax};
      }
    };

    \coordinate (level\level sampleminlabel)
    at (level\level samplemin\levelblocks);
    \coordinate (level\level samplemeanlabel)
    at (level\level samplemean\levelblocks);
    \coordinate (level\level samplemaxlabel)
    at (level\level samplemax\levelblocks);
  };

  % arrows
  \foreach \next in {2,...,\levels} {
    \pgfmathtruncatemacro{\level}{\next-1}
    \pgfmathsetmacro{\amplitude}{3pt * \level + 1.5pt}
    \pgfmathsetmacro{\thislevelblocks}{\blocks / (4^(\level-1))}
    \pgfmathsetmacro{\nextlevelblocks}{\blocks / (4^(\level))}
    \foreach \block in {1,...,\nextlevelblocks} {
      \pgfmathtruncatemacro{\a}{4*(\block-1)+1}
      \pgfmathtruncatemacro{\b}{4*(\block-1)+4}
      \pgfmathtruncatemacro{\c}{4*(\block-1)+2}
      \draw [thick, decorate, decoration={brace, amplitude=\amplitude, mirror}]
      ([xshift=0.5pt]level\level samplemax\a.south west) --
      ([xshift=-0.5pt]level\level samplemax\b.south east);
      \draw[thick, -stealth]
      ([yshift=-\amplitude]level\level samplemax\c.south east) --
      (level\next samplemin\block .north);
    };
  };

  % text
  \foreach \level in {1,...,\levels} {
    \pgfmathtruncatemacro{\decim}{(4^(\level - 1))}
    % Level N
    \node[xshift=-2.5cm, yshift=6pt, anchor=west] (foo) at
    ($(level\level sample0 |- level\level samplemean1)$)
    {Level \level};
    % Samples
    \node[anchor=north, inner sep=0, font=\footnotesize] at (foo.south)
    {\ifnumequal{\level}{1}{(${\color{red}N}$ values)}
      {($3\cdot {\color{red}N / \decim}$ values)}};
  };

  \begin{scope}[anchor=west, inner sep=0, font=\footnotesize\itshape,
    text depth=0ex, text height=1.1ex, draw]
    \foreach \level in {2,...,\levels} {
      \node[xshift=3pt] at (level\level sampleminlabel) { min };
      \node[xshift=3pt] at (level\level samplemeanlabel) { mean };
      \node[xshift=3pt] at (level\level samplemaxlabel) { max };
    };
  \end{scope}

  \node[yshift=-0.8cm] at (foo.south) { $\vdots$ };

\end{tikzpicture}
\end{document}