title: Fill transition in gganimate
body: <p>I want to animate a fill value transition between states. I have a 100x100 grid of geom_points that take values between 0 and 1. Essentially, the points stay in the same position at every point in time, but their fill value changes, which I want to animate. Here an excerpt on the data</p>
  <pre><code>head(strg)
  
          Var1      Var2 const4       pred id
     1 -1.0000000   -1      1 3.337224e-37  1
     2 -0.9292929   -1      1 1.922538e-34  2
     3 -0.8585859   -1      1 2.561529e-32  3
     4 -0.7878788   -1      1 2.522569e-30  4
     5 -0.7171717   -1      1 1.433660e-28  5
     6 -0.6464646   -1      1 1.795601e-27  6
  </code></pre>
  <p>where const4 takes on the different states. And here the initial plot</p>
  <pre><code>ggplot(strg, aes(x = strg[,1], y = strg[,2])) + geom_point(aes(color = strg[,&quot;pred&quot;])) + scale_color_gradient(&quot;Predictions&quot;, low = &quot;blue&quot;, high = &quot;orange&quot;)
  </code></pre>
  <p>My questions are now</p>
  <ol>
  <li>How do I have to structure my data frame upon which the ggplot is build? I thought about having it repeat for all the states in const4.</li>
  <li>What function to use in gganimate to visualize the tranisition?</li>
  </ol>