title: Variable(s)have been specified in ‘linfct’ but cannot be found in ‘model’!
body: <p>I want to run a multiple comparisons analysis for the different variables of a model. My idea is as follows:</p>
  
  <pre><code>a
     V1   V2
  1  t1  5.0
  2  t1  4.0
  3  t1  2.0
  4  t1  5.0
  5  t1  5.0
  6  t2  4.0
  7  t2  3.0
  8  t2  4.0
  9  t2  9.0
  10 t2  3.0
  11 t3  2.0
  12 t3  3.0
  13 t3  2.0
  14 t3  6.0
  15 t3  8.0
  
  tuk&lt;-glht(fit,linfct=mcp(a$V1="Tukey"))
  </code></pre>
  
  <p>when I run， it showed :</p>
  
  <pre><code>“Variable(s) ‘trt’ have been specified in ‘linfct’ but cannot be found in ‘model’!”
  </code></pre>
  
  <p>I don't know how to deal with it。</p>