title: making Boxplot with 3 variables in r
body: <p>I want to make a boxplot in r but I struggle with grouping the boxplot﻿ by a third variable. </p>
  
  <p>I want to have boxplots- all on one y-axes (score on a treatment outcome questionnaire), called HAMD)) -</p>
  
  <p>for weeks 0-5 (called week)</p>
  
  <p>and all twice for two treatment groups (called Treatment).</p>
  
  <p>I made two boxplots with</p>
  
  <blockquote>
    <p>boxplot(MP$HAMD ~ MP$week)</p>
  </blockquote>
  
  <p>and six with</p>
  
  <blockquote>
    <p>boxplot(MP$HAMD ~ MP$Treatment)</p>
  </blockquote>
  
  <p>But now I want 12 boxplots together, each per week per treatment.
  How can I do this in r?</p>
  
  <p>By all means thank you very much.</p>