Drawing grids filled with random selected colors and connecting them

Question

What I'm trying to do is to draw to 4 x 4 grids side-by-side to represent the concept of bootstrap, from statistics.

So, what I would like to do is to draw them and fill each cell of each grid with a random color chosen from a predefined set of colors.

After that, I would like to connect the grids with an arrow centered on the y middle of them with and the x positioned at the right and left border of them, respectively.

This is an example of what I would like to achieve:

This is my current approach:

\documentclass[11pt,a4paper]{article}

\usepackage{tikz}

\begin{figure}[htb]
\begin{tikzpicture}[scale=.7]

    \begin{scope}
        \draw (0, 0) grid (4, 4);
        \coordinate (input);
    \end{scope}

    \begin{scope}[xshift=7cm] 
        \draw (0, 0) grid (4, 4);
        \coordinate (output);
    \end{scope}  

    \draw[-latex, thick, red!80] (input) -- (output) node [pos=0.5,above,font=\footnotesize] {output};

\end{tikzpicture}
\end{figure}

\end{document}

However, I'm far from what I would like:

How should I proceed?

Thank you.

Answer 1

I would suggest you use the to syntax instead of the -- for connecting the squares. For coloring the squares you can define a list of colors via \pgfmathdeclarerandomlist:

Notes:

• I used tikz's calc library to get the midpoint of the squares.

Code:

\documentclass[11pt,a4paper]{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\pgfmathdeclarerandomlist{MyRandomColors}{%
    {red}%
    {red!25}%
    {magenta}%
    {magenta!25}%
    {olive}%
    {olive!25}%
    {brown}%
    {brown!10}%
    {violet}%
    {violet!25}%
    {gray}%
    {purple}%
    {yellow}%
    {orange}%
    {orange!25}%
    {cyan}%
    {green}%

}%
\newcommand*{\GridSize}{4}
\newcommand*{\ColorCells}{%
    \foreach \y in {1,...,\GridSize} {
        \foreach \x in {1,...,\GridSize} {
            \pgfmathrandomitem{\RandomColor}{MyRandomColors} 
            \draw [fill=\RandomColor, fill opacity=0.4, draw=none, ultra thick] 
                (\x-1,\y-1) rectangle (\x,\y);
        }%
    }%
}%
\listfiles
\begin{document}
\begin{tikzpicture}[scale=.7]
\begin{scope}[thick]
    \ColorCells
    \draw (0, 0) grid (\GridSize, \GridSize);
    \coordinate (input);
\end{scope}

\begin{scope}[thick, xshift=7cm] 
    \ColorCells
    \draw (0, 0) grid (\GridSize, \GridSize);
    \coordinate (output);
\end{scope}  

\draw[-latex, ultra thick, red!80] 
    ($(input)+(2.5,2.5)$) to[out=0, in=180] 
        node [pos=0.5,sloped, above,font=\footnotesize] {output}
    ($(output)+(1.5,1.5)$) 
        ;


\end{tikzpicture}
\end{document}

Answer 2

The code uses 7 colors. Of course, this can be modified (the number and/or the colors) by changing the command \rcolor which produces, for each integer in between 1 and 7, one of the colors. The integer is created randomly when the grid is drawn.

I defined the colors separately, at the beginning. It is easier to modify them this way.

\documentclass[11pt, margin=1cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows, calc, math, arrows.meta}
\xdefinecolor{sR}{RGB}{238, 4, 34}
\xdefinecolor{sO}{RGB}{255, 102, 17}
\xdefinecolor{sY}{RGB}{238, 204, 17}
\xdefinecolor{sW}{RGB}{230, 240, 235}
\xdefinecolor{sC}{RGB}{17, 170, 187}
\xdefinecolor{sB}{RGB}{17, 87, 221}
\definecolor{sV}{RGB}{153, 0, 238}
\newcommand{\rcolor}[1]{%
  \ifnum#1=1 sR%
  \else\ifnum#1=2 sO%
  \else\ifnum#1=3 sY%
  \else\ifnum#1=4 sW%
  \else\ifnum#1=5 sC%
  \else\ifnum#1=6 sB%
  \else\ifnum#1=7 sV%
  \fi\fi\fi\fi\fi\fi\fi%
}
\begin{document}
\tikzmath{%  controls the distance between the two grids
  real \d; \d = 6.;
  int \tmp;
}
\begin{tikzpicture}[scale=1.2]
  \foreach \i in {0,...,3}{%
    \foreach \j in {0,...,3}{%
      \tikzmath{\tmp = random(1, 7);}
      \draw[fill=\rcolor{\tmp}!70, shift={(-2, -2)}]
      (\i,\j) rectangle ++(1, 1);
    }
  }
  \foreach \i in {0, 1, 2, 3}{%
    \foreach \j in {0, 1, 2, 3}{%
      \tikzmath{\tmp = random(1, 7);}
      \draw[fill=\rcolor{\tmp}!70, shift={(\d, -2)}]
      (\i, \j) rectangle ++(1, 1);
    }
  }
  \draw[sR!60!black, -{Latex[length=7pt, width=5pt]}, thick]
  (2.2, 0) -- node[pos=.5, above] {output} (\d-.2, 0);
\end{tikzpicture}
\end{document}