Otdfbt

I'm using beamer and I have a randomly colored grid (three colors, 4 x 19 grid) on the slides. Since I use the pause command, it generates a new grid every time I click to the next point. How do I force it to remember the first grid it generated? I know it should be something with redefining the color after the first generated grid (maybe edef?).

So this is my code for the grid:

documentclass[a4paper,12pt]beamer
usepackagetikz
usetikzlibrarycalc

pgfmathdeclarerandomlistMyRandomColors%
red%
blue%
green%


begindocument
begintikzpicture[x=0.6cm,y=0.8cm]
foreach x in 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18
foreach y in 0,1,2,3

 pgfmathrandomitemRandomColorMyRandomColors 
 draw[RandomColor, fill=RandomColor] (x,y) circle (0.2cm);

endtikzpicture
enddocument

A simple way is to save the grid to a box:

documentclass[a4paper,12pt]article
usepackagetikz
usetikzlibrarycalc

begindocument

newboxmygrid
saveboxmygrid%
begintikzpicture[x=0.6cm,y=0.8cm]
foreach x in 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18
foreach y in 0,1,2,3

 pgfmathrandomitemRandomColorMyRandomColors 
 draw[RandomColor, fill=RandomColor] (x,y) circle (0.2cm);

endtikzpicture
 

%when you want to use the grid, you just call usebox

useboxmygrid

enddocument

You may also place the box within a node for placement control.

Specifying a seed pgfmathsetseed1 within your tikzpicture should fix the problem.

documentclass[10pt,a4paper]beamer
usepackagetikz
usetikzlibrarycalc

pgfmathdeclarerandomlistMyRandomColors%
 red%
 blue%
 green%


begindocument
 beginframe
 begintikzpicture[x=0.6cm,y=0.8cm]
 pgfmathsetseed1%
 foreach x in 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18
 foreach y in 0,1,2,3
 
 pause
 pgfmathrandomitemRandomColorMyRandomColors 
 draw[RandomColor, fill=RandomColor] (x,y) circle (0.2cm);
 
 endtikzpicture
 endframe

enddocument

Alternatively to saving the grid in a box, you could compute the random color order only once and use it when creating the grid:

documentclassarticle

usepackagetikz
usetikzlibrarycalc

usepackageetoolbox

pgfmathdeclarerandomlistMyRandomColors%
 red%
 blue%
 green%


makeatletter
 defcolorrows@gobble
 foreach row in 0,...,3 
 defcolors@gobble
 foreach col in 0,...,18 
 pgfmathrandomitemrandomcolorMyRandomColors
 xapptocolors,randomcolor
 
 xapptocolorrows,colors
 
 edefcolorrowscolorrows
makeatother

begindocument

begintikzpicture [x=0.6cm, y=0.8cm]
 foreach row [count=y] in colorrows 
 foreach col [count=x] in row 
 draw [col, fill=col] (x,y) circle (0.2cm);
 
 
endtikzpicture

enddocument

The @gobbles get rid of the first comma added by each loop.