title: Grouped bar plot in ggplot with y values based on combination of 2 categorical variables?
body: <p>I am trying to create a grouped bar plot in ggplot, in which there should be 4 bars per each x value. Here is a subset of my data (actual data is about 4x longer):</p>
  
  <pre><code>Verb_Type,Frame,proportion_type,speaker
  mental,V CP,0.209513024,Child
  mental,V NP,0.138731597,Child
  perception,V CP,0.017167382,Child
  perception,V NP,0.387528402,Child
  mental,V CP,0.437998087,Parent
  mental,V NP,0.144086707,Parent
  perception,V CP,0.042695836,Parent
  perception,V NP,0.398376853,Parent
  </code></pre>
  
  <p>What I want is to plot Frame as the x values and proportion_type as the y values, but with the bars based on both Verb_Type and speaker. So for each x value (Frame), there would be 4 bars grouped together - a bar each for the proportion_type value corresponding to mental~child, mental~parent, perception~child, perception~parent. I need for the fill color to be based on Verb_Type, and the fill "texture" (saturation or something) based on speaker. I do <em>not</em> want stacked bars, as it would not accurately represent the data. </p>
  
  <p>I don't want to use facet grids because I find it visually difficult to compare all 4 bars when they're separated into 2 groups. I want to group all the bars together so that the visualization is easier. But I can't figure out how to make the appropriate groupings. Is this something I can do in ggplot, or do I need to manipulate the data before plotting? I tried using melt to reshape the data, but either I was doing it wrong, or that's not what I actually should be doing. </p>