title: party package for decision tree in R does not support character data type?
body: <p>If one of the columns in my data frame is of data type character, I get the error below.</p>
  
  <pre><code>&gt; library("party")
  &gt; r2 &lt;- ctree(Sepal.Length ~ .,data=df)
  Error in trafo(data = data, numeric_trafo = numeric_trafo, factor_trafo = factor_trafo,  : 
    data class character is not supported
  &gt; plot(r2)    
  &gt; sapply(df,class)
  Sepal.Length  Sepal.Width Petal.Length  Petal.Width      Species 
      "factor"     "factor"     "factor"  "character"     "factor" 
  </code></pre>
  
  <p>Sometimes, I also get this error</p>
  
  <pre><code> Error in match.arg(type) : 
    'arg' should be one of “response”, “node”, “prob” &gt; 
  &gt; sapply(df,class)
            AGE        GENDER          STAY      GRADE          XYNS        CHARGE 
      "integer"     "integer"      "factor"     "integer"     "integer"     "integer" 
  </code></pre>
  
  <p>How do I get around these?</p>