title: How do I turn this pgf plot adjacent bar chart with two y axis labels
body: <p>I have the following code which roughly approximates a diagram I want to make with tikz:</p>
  
  <pre><code>\begin{tikzpicture}
  \begin{axis}[
  % (normal text should not be set in math mode)
  xlabel=,
  ylabel=,
  % if you use `data' ticks will be set on every x coordinate that is
  % given by the *first* `\addplot' command
  xtick=data,
  xticklabels={
      Control,
      Voucher,
      Transfer%
  },
  ytick=data,
  yticklabels={
      No increase,
      Increase%
  },
  % use the following key so the baseline of all ticklabel entries is the same
  % (compare this image to the one from marmot)
  typeset ticklabels with strut,
  % there is one default value for the `legend pos' that is outside the axis
  legend pos=outer north east,
  % (so the legend looks a bit better)
  legend cell align=left,
  % (moved this common key here),
  ]
  % (renamed `plot coordinates' by `coordinates'
  \addplot [mark=*,blue] coordinates {
      (1,1)
      (2,1)
      (3,1)
  };
  
  \addplot [color=red,mark=x] coordinates {
      (1,1)
      (2,1)
      (3,2)
  };
  
  \addplot [color=green,mark=x] coordinates {
      (1,1)
      (2,2)
      (3,2)
  };
  
  % (replaced `\addlegendentry's with `\legend')
  \legend{
      Pure Altruism,
      Warm Glow,
      Mental Accounting,
  }
  \end{axis}
  \end{tikzpicture}
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/E6Em7.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/E6Em7.png" alt="enter image description here"></a></p>
  
  <p>As you can see, I have attempted to add y axis tick labels, but this has not emerged in the actual diagram itself. Further, what I am trying to illustrate is discrete in nature, so I want there to be three adjacent bars for each tick on the x axis that will illustrate whether the level should be 'high' or 'low' under each of the theories in the legend.</p>
  
  <p>How can I convert this to a bar chart with three adjacent bars and add the two y axis labels I need?</p>