title: Combine corpora in tm 0.7.3
body: <p>Using the text mining package <code>tm</code> for R, the following works in version 0.6.2, R version 3.4.3:</p>
  
  <pre><code>library(tm)
  a = "This is the first document."
  b = "This is the second document."
  c = "This is the third document."
  d = "This is the fourth document."
  docs1 = VectorSource(c(a,b))
  docs2 = VectorSource(c(c,d))
  corpus1 = Corpus(docs1)
  corpus2 = Corpus(docs2)
  corpus3 = c(corpus1,corpus2)
  inspect(corpus3)
  &lt;&lt;VCorpus&gt;&gt;
  Metadata:  corpus specific: 0, document level (indexed): 0
  Content:  documents: 4
  </code></pre>
  
  <p>However, the same code in <code>tm</code> version 0.7.3  (R version 3.4.2) gives an error:</p>
  
  <pre><code>Error in UseMethod("inspect", x) :
    no applicable method for 'inspect' applied to an object of class "list"
  </code></pre>
  
  <p>According to <code>vignette("tm",package="tm")</code>, the <code>c()</code> function is overloaded:</p>
  
  <blockquote>
    <p>Many standard operators and functions (<code>[, [&lt;-, [[, [[&lt;-, c(), lapply()</code>) are available for corpora with semantics similar to standard
    R routines. E.g., <code>c()</code> concatenates two (or more) corpora. Applied to
    several text documents it returns a corpus. The metadata is
    automatically updated, if corpora are concatenated (i.e., merged).</p>
  </blockquote>
  
  <p>However, for the new version this is apparently no longer the case. How can two corpora be combined in <code>tm</code> 0.7.3? An obvious solution is to combine the documents first and create the corpus afterwards, but I'm looking for a solution to combine two already existing corpora.</p>